Here below some basic MCQ’s about “Laws of chemical combination” with answer which is explained in details. Let’s check one by one which is given below.
MCQ 1
Which of the following statements is a reflection of the Law of Conservation of Mass?
A) Mass can be created or destroyed in a chemical reaction.
B) The total mass of reactants is equal to the total mass of products.
C) Atoms can be converted into energy.
D) Only certain elements can combine chemically.
Answer: B) The total mass of reactants is equal to the total mass of products.
Explanation: The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. Thus, the mass of the reactants must equal the mass of the products.
MCQ 2
The Law of Definite Proportions states that:
A) Elements combine in fixed ratios to form compounds.
B) The mass of the products is equal to the mass of the reactants.
C) The same compound can have different ratios in different reactions.
D) Chemical reactions involve the rearrangement of atoms.
Answer: A) Elements combine in fixed ratios to form compounds.
Explanation: The Law of Definite Proportions, also known as Proust’s Law, states that a chemical compound always contains the same proportion of elements by mass, regardless of the amount of the compound or its source.
MCQ 3
Which law explains why water (H₂O) always has a composition of 2 hydrogen atoms for every 1 oxygen atom?
A) Law of Multiple Proportions
B) Law of Conservation of Mass
C) Law of Definite Proportions
D) Avogadro’s Law
Answer: C) Law of Definite Proportions.
Explanation: The Law of Definite Proportions states that a chemical compound is composed of the same elements in the same proportions by mass, which is why water always has a consistent composition of 2 hydrogen atoms for every 1 oxygen atom.
MCQ 4
According to the Law of Multiple Proportions, when two elements combine to form different compounds, the masses of one element that combine with a fixed mass of the other element are in:
A) Equal ratios.
B) Whole number ratios.
C) Variable ratios.
D) Proportional to their atomic masses.
Answer: B) Whole number ratios.
Explanation: The Law of Multiple Proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element can be expressed as a ratio of small whole numbers.
MCQ 5
What is the correct statement according to Dalton’s Atomic Theory?
A) Atoms of different elements can combine in any ratio.
B) Atoms are indivisible and indestructible.
C) All atoms of the same element have different masses.
D) Atoms can change from one element to another during chemical reactions.
Answer: B) Atoms are indivisible and indestructible.
Explanation: Dalton’s Atomic Theory posits that atoms are the fundamental building blocks of matter and are indivisible in chemical processes. It also states that atoms of the same element are identical in mass and properties.
MCQ 6
Which law states that when two elements form a compound, they do so in fixed proportions by mass?
A) Law of Definite Proportions
B) Law of Conservation of Mass
C) Law of Multiple Proportions
D) Dalton’s Law
Answer: A) Law of Definite Proportions.
Explanation: This law indicates that a chemical compound always contains its component elements in fixed mass ratios.
MCQ 7
In the reaction of hydrogen and oxygen to form water, which law is illustrated?
A) Law of Conservation of Mass
B) Law of Multiple Proportions
C) Law of Definite Proportions
D) Avogadro’s Law
Answer: A) Law of Conservation of Mass.
Explanation: This law is illustrated as the total mass of hydrogen and oxygen before the reaction equals the mass of water produced.
MCQ 8
Which of the following compounds exemplifies the Law of Multiple Proportions?
A) H₂O
B) CO₂ and CO
C) NaCl
D) CH₄
Answer: B) CO₂ and CO.
Explanation: Carbon can combine with oxygen in different ratios to form CO and CO₂, demonstrating the Law of Multiple Proportions.
MCQ 9
According to Avogadro’s Law, equal volumes of gases at the same temperature and pressure contain:
A) Equal masses.
B) Equal numbers of molecules.
C) Different types of molecules.
D) Different volumes.
Answer: B) Equal numbers of molecules.
Explanation: Avogadro’s Law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules.
MCQ 10
What happens to the mass during a chemical reaction according to the Law of Conservation of Mass?
A) It increases.
B) It decreases.
C) It remains constant.
D) It becomes energy.
Answer: C) It remains constant.
Explanation: The Law of Conservation of Mass states that mass is conserved in a chemical reaction; it neither increases nor decreases.
MCQ 11
Which of the following is NOT a postulate of Dalton’s Atomic Theory?
A) Atoms are indivisible.
B) All atoms of a given element are identical.
C) Atoms can be created or destroyed.
D) Atoms combine in simple whole-number ratios.
Answer: C) Atoms can be created or destroyed.
Explanation: Dalton’s theory posits that atoms cannot be created or destroyed in chemical reactions.
MCQ 12
What is the ratio of masses of nitrogen in N₂ and N₃H?
A) 1:3
B) 2:3
C) 3:2
D) 3:1
Answer: B) 2:3.
Explanation: In N₂, nitrogen has a mass of 28 g (2 x 14), while in N₃H, the nitrogen mass is 42 g (3 x 14). The ratio is 28:42 or 2:3.
MCQ 13
The concept of atomic weights was first introduced by:
A) John Dalton
B) Dmitri Mendeleev
C) Antoine Lavoisier
D) J.J. Thomson
Answer: A) John Dalton.
Explanation: Dalton introduced the concept of atomic weights in his atomic theory, helping to establish relative masses of atoms.
MCQ 14
What is the primary assumption of the Law of Conservation of Mass?
A) Mass can be transformed into energy.
B) Mass can be created from nothing.
C) Mass remains constant in a closed system.
D) Mass can change forms.
Answer: C) Mass remains constant in a closed system.
Explanation: This law states that the mass of a closed system remains unchanged during a chemical reaction.
MCQ 15
In a chemical reaction, if 10 g of reactant A reacts with 20 g of reactant B to produce product C, how much product C is formed?
A) 10 g
B) 20 g
C) 30 g
D) 0 g
Answer: C) 30 g.
Explanation: According to the Law of Conservation of Mass, the mass of products equals the mass of reactants.
MCQ 16
Which law states that if two elements can form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole number ratios?
A) Law of Conservation of Mass
B) Law of Definite Proportions
C) Law of Multiple Proportions
D) Dalton’s Law
Answer: C) Law of Multiple Proportions.
Explanation: This law highlights how different compounds formed by two elements are related by simple whole number ratios.
MCQ 17
What does the Law of Definite Proportions imply for the compound NaCl?
A) It can contain different ratios of sodium and chlorine.
B) It always contains 1 part sodium and 1 part chlorine by mass.
C) It has a constant composition of sodium and chlorine.
D) It can exist in different forms.
Answer: C) It has a constant composition of sodium and chlorine.
Explanation: This law states that NaCl always consists of sodium and chlorine in the same fixed ratio.
MCQ 18
Which of the following compounds violates the Law of Definite Proportions?
A) H₂O
B) CO₂
C) C₆H₁₂O₆
D) H₂O₂ and H₂O
Answer: D) H₂O₂ and H₂O.
Explanation: H₂O and H₂O₂ contain different ratios of hydrogen to oxygen, illustrating that different compounds can have varying compositions.
MCQ 19
What does a balanced chemical equation ensure?
A) The mass of reactants equals the mass of products.
B) The rate of reaction is constant.
C) The number of atoms of each element is unequal.
D) The temperature remains unchanged.
Answer: A) The mass of reactants equals the mass of products.
Explanation: A balanced chemical equation confirms that the mass and number of atoms are conserved during the reaction.
MCQ 20
According to the Law of Conservation of Mass, if 5 g of hydrogen reacts with 8 g of oxygen, how much water is produced?
A) 5 g
B) 8 g
C) 13 g
D) 0 g
Answer: C) 13 g.
Explanation: The total mass of the reactants (5 g + 8 g) equals the mass of the product (water), which is 13 g.
MCQ 21
Which of the following is an example of a chemical change?
A) Melting of ice
B) Dissolving sugar in water
C) Rusting of iron
D) Boiling of water
Answer: C) Rusting of iron.
Explanation: Rusting is a chemical change as it involves a reaction between iron and oxygen, producing rust (iron oxide).
MCQ 22
In the chemical formula for water (H₂O), what does the “2” represent?
A) The total number of atoms
B) The number of oxygen atoms
C) The number of hydrogen atoms
D) The ratio of hydrogen to oxygen
Answer: C) The number of hydrogen atoms.
Explanation: The “2” indicates that there are two hydrogen atoms for every one oxygen atom in a water molecule.
MCQ 23
According to Dalton’s Atomic Theory, which of the following is true about atoms?
A) Atoms can be created and destroyed.
B) Atoms of the same element are identical in mass and properties.
C) Atoms are divisible into smaller particles.
D) Atoms can exist in various states of matter.
Answer: B) Atoms of the same element are identical in mass and properties.
Explanation: Dalton stated that all atoms of a given element are identical, which is a key component of his atomic theory.
MCQ 24
What is the molar mass of water (H₂O)?
A) 18 g/mol
B) 16 g/mol
C) 20 g/mol
D) 10 g/mol
Answer: A) 18 g/mol.
Explanation: The molar mass of water is calculated as 2 (H) + 1 (O) = 2(1) + 16 = 18 g/mol.
MCQ 25
Which law explains why chemical formulas for compounds must reflect the actual composition?
A) Law of Definite Proportions
B) Law of Conservation of Mass
C) Law of Multiple Proportions
D) Dalton’s Law
Answer: A) Law of Definite Proportions.
Explanation: This law states that a chemical compound always contains its constituent elements in fixed proportions by mass, guiding the formulation of chemical formulas.
MCQ 26
Which of the following compounds is formed by the Law of Multiple Proportions?
A) H₂O and H₂O₂
B) CO and CO₂
C) NaCl and Na₂S
D) Both A and B
Answer: D) Both A and B.
Explanation: Both pairs of compounds are formed by two elements that can combine in different ratios to form different compounds.
MCQ 27
What is the primary focus of the Law of Conservation of Mass?
A) Energy changes in reactions
B) The balance of elements in compounds
C) The mass of reactants and products
D) The physical states of matter
Answer: C) The mass of reactants and products.
Explanation: This law specifically states that the mass remains constant during a chemical reaction, focusing on the total mass of reactants and products.
MCQ 28
If 6 g of carbon reacts with 16 g of oxygen to form carbon dioxide, what is the mass of carbon dioxide produced?
A) 10 g
B) 16 g
C) 22 g
D) 0 g
Answer: C) 22 g.
Explanation: The mass of carbon dioxide produced is equal to the total mass of reactants: 6 g + 16 g = 22 g.
MCQ 29
According to the Law of Definite Proportions, which of the following is a true statement?
A) H₂ and O₂ combine in a 2:1 ratio to form water.
B) Water can be made from different ratios of hydrogen and oxygen.
C) A given compound always contains the same proportion of elements by mass.
D) All compounds have the same chemical properties.
Answer: C) A given compound always contains the same proportion of elements by mass.
Explanation: This law emphasizes that the composition of a chemical compound is constant, regardless of its source.
MCQ 30
Which of the following reactions demonstrates the Law of Conservation of Mass?
A) Synthesis of water from hydrogen and oxygen
B) Decomposition of water into hydrogen and oxygen
C) Combustion of methane
D) All of the above
Answer: D) All of the above.
Explanation: Each of these reactions adheres to the Law of Conservation of Mass, where the total mass of reactants equals the total mass of products.
MCQ 31
What does a balanced chemical equation represent?
A) The energy changes during a reaction
B) The physical states of reactants and products
C) The conservation of mass
D) The rates of reaction
Answer: C) The conservation of mass.
Explanation: A balanced equation indicates that the number of atoms of each element is conserved, reflecting the Law of Conservation of Mass.
MCQ 32
In the chemical formula C₆H₁₂O₆, what does the “6” before carbon signify?
A) The number of carbon atoms
B) The mass of carbon
C) The number of oxygen atoms
D) The total number of atoms
Answer: A) The number of carbon atoms.
Explanation: The “6” indicates that there are six carbon atoms in the glucose molecule.
MCQ 33
Which of the following statements about the Law of Conservation of Mass is true?
A) It applies only to physical changes.
B) It was first formulated by Albert Einstein.
C) It states that mass can be converted into energy.
D) It applies to all chemical reactions.
Answer: D) It applies to all chemical reactions.
Explanation: The Law of Conservation of Mass is applicable to all chemical reactions, emphasizing that mass remains constant.
MCQ 34
Which of the following describes a fixed ratio in the context of chemical compounds?
A) H₂ and O₂ combine in a variable ratio.
B) NaCl always contains 1:1 ratio of sodium to chlorine.
C) All molecules have different ratios of atoms.
D) Elements can combine in any ratio.
Answer: B) NaCl always contains 1:1 ratio of sodium to chlorine.
Explanation: The composition of NaCl is fixed, always comprising one sodium atom for each chlorine atom.
MCQ 35
What is the outcome when nitrogen and hydrogen react to form ammonia?
A) Fixed mass is lost.
B) New elements are formed.
C) Mass is conserved.
D) Energy is destroyed.
Answer: C) Mass is conserved.
Explanation: In the reaction between nitrogen and hydrogen to form ammonia, the total mass of the reactants equals the total mass of ammonia produced.
MCQ 36
What does the Law of Multiple Proportions apply to?
A) Mixtures of elements
B) Different compounds formed from the same elements
C) Physical changes only
D) The states of matter
Answer: B) Different compounds formed from the same elements.
Explanation: This law pertains to how two elements can combine in different ratios to form various compounds.
MCQ 37
When sodium reacts with chlorine, what is the resulting compound?
A) NaCl
B) NaCl₂
C) Na₂Cl
D) Na₂Cl₂
Answer: A) NaCl.
Explanation: Sodium and chlorine react in a 1:1 ratio to form sodium chloride (NaCl).
MCQ 38
Which of the following is an implication of Dalton’s Atomic Theory?
A) All substances are made of molecules.
B) Atoms can be split into smaller parts.
C) Chemical reactions involve the rearrangement of atoms.
D) Elements can vary in their atomic weights.
Answer: C) Chemical reactions involve the rearrangement of atoms.
Explanation: Dalton’s theory states that atoms are rearranged during chemical reactions, which supports the idea of conservation of mass.
MCQ 39
What principle underlies stoichiometry in chemical reactions?
A) Law of Conservation of Energy
B) Law of Definite Proportions
C) Law of Multiple Proportions
D) Law of Conservation of Mass
Answer: D) Law of Conservation of Mass.
Explanation: Stoichiometry is based on the principle that mass is conserved in chemical reactions, allowing the calculation of reactants and products.
MCQ 40
What does the term “stoichiometry” refer to?
A) The study of the properties of gases
B) The calculation of reactants and products in chemical reactions
C) The relationship between temperature and pressure
D) The measurement of physical changes
Answer: B) The calculation of reactants and products in chemical reactions.
Explanation: Stoichiometry involves the quantitative relationships between the substances involved in a chemical reaction.
MCQ 41
What is the mass ratio of hydrogen to oxygen in water (H₂O)?
A) 1:16
B) 2:16
C) 1:8
D) 1:2
Answer: C) 1:8.
Explanation: The mass of hydrogen (2 g) to oxygen (16 g) in water is 1:8.
MCQ 42
Which statement best describes the Law of Conservation of Mass?
A) Energy is transformed during reactions.
B) Atoms are rearranged but not created or destroyed.
C) Compounds can form in any ratio.
D) Mass can disappear during reactions.
Answer: B) Atoms are rearranged but not created or destroyed.
Explanation: This law states that during a chemical reaction, atoms are rearranged, but the total mass remains constant.
MCQ 43
Which of the following is an example of a synthesis reaction?
A) Decomposition of calcium carbonate
B) Combustion of methane
C) Formation of water from hydrogen and oxygen
D) Reaction of zinc with hydrochloric acid
Answer: C) Formation of water from hydrogen and oxygen.
Explanation: A synthesis reaction involves two or more reactants combining to form a single product, like water.
MCQ 44
Which of the following best describes a compound?
A) A mixture of elements
B) A substance formed by a fixed ratio of atoms
C) An element in its pure form
D) A physical combination of different substances
Answer: B) A substance formed by a fixed ratio of atoms.
Explanation: A compound is formed when two or more elements chemically combine in a fixed ratio.
MCQ 45
Which law states that different compounds can be formed from the same elements?
A) Law of Definite Proportions
B) Law of Multiple Proportions
C) Law of Conservation of Mass
D) Dalton’s Law
Answer: B) Law of Multiple Proportions.
Explanation: This law indicates that elements can combine in different ratios to form various compounds.
MCQ 46
In a balanced chemical equation, the coefficients represent:
A) The number of molecules involved.
B) The types of atoms present.
C) The physical states of reactants and products.
D) The energy changes during the reaction.
Answer: A) The number of molecules involved.
Explanation: Coefficients in a balanced equation indicate the relative number of molecules or moles of each substance.
MCQ 47
What is the main consequence of not balancing a chemical equation?
A) It can lead to incorrect calculations of mass.
B) It shows no relationship between reactants and products.
C) It prevents the reaction from occurring.
D) It changes the physical states of reactants.
Answer: A) It can lead to incorrect calculations of mass.
Explanation: An unbalanced equation does not accurately reflect the conservation of mass, leading to incorrect mass calculations.
MCQ 48
How many grams of oxygen are required to completely react with 2 grams of hydrogen to form water?
A) 8 g
B) 16 g
C) 2 g
D) 4 g
Answer: B) 16 g.
Explanation: The reaction H₂ + ½O₂ → H₂O shows that 2 g of hydrogen requires 16 g of oxygen for complete reaction.
MCQ 49
Which of the following compounds shows a 1:1 ratio of elements?
A) H₂O
B) NH₃
C) CO
D) CH₄
Answer: C) CO.
Explanation: Carbon monoxide (CO) has a 1:1 ratio of carbon to oxygen atoms.
MCQ 50
What does the Law of Definite Proportions ensure about a compound?
A) Its elements can vary in proportion.
B) It will always have the same mass ratio of its elements.
C) Its properties change with the source.
D) It can exist in multiple forms.
Answer: B) It will always have the same mass ratio of its elements.
Explanation: This law guarantees that a compound has a fixed composition regardless of its source.
MCQ 51
In a reaction where 5 g of substance A combines with 10 g of substance B to form 12 g of substance C, what happens to the mass?
A) Mass is lost.
B) Mass is gained.
C) Mass is conserved.
D) Mass is doubled.
Answer: C) Mass is conserved.
Explanation: According to the Law of Conservation of Mass, the total mass of reactants equals the total mass of products.
MCQ 52
If two elements combine in different ratios to form different compounds, which law is demonstrated?
A) Law of Conservation of Mass
B) Law of Definite Proportions
C) Law of Multiple Proportions
D) Dalton’s Law
Answer: C) Law of Multiple Proportions.
Explanation: This law illustrates that two elements can combine in various ratios to create different compounds.
MCQ 53
What is the molar mass of carbon dioxide (CO₂)?
A) 22 g/mol
B) 28 g/mol
C) 44 g/mol
D) 12 g/mol
Answer: C) 44 g/mol.
Explanation: The molar mass is calculated as 12 (C) + 2(16) (O) = 44 g/mol.
MCQ 54
Which statement describes the Law of Conservation of Mass?
A) Energy is neither created nor destroyed.
B) The number of protons does not change in a reaction.
C) Matter can change forms, but total mass remains constant.
D) Compounds can only form from elements in a fixed ratio.
Answer: C) Matter can change forms, but total mass remains constant.
Explanation: This law states that while the forms of matter may change, the total mass before and after a reaction remains unchanged.
MCQ 55
What is the empirical formula for C₆H₁₂O₆?
A) CH₂O
B) C₂H₄O₂
C) C₆H₁₂O₆
D) C₁H₁O₁
Answer: A) CH₂O.
Explanation: The empirical formula represents the simplest whole number ratio of elements, which is CH₂O for glucose.
MCQ 56
What happens to the atoms in a chemical reaction according to Dalton’s Atomic Theory?
A) They are destroyed.
B) They are created.
C) They are rearranged.
D) They change their identity.
Answer: C) They are rearranged.
Explanation: Atoms are not created or destroyed but rearranged during chemical reactions.
MCQ 57
What do the subscripts in a chemical formula indicate?
A) The temperature of the substance
B) The state of the substance
C) The number of atoms of each element
D) The energy level of electrons
Answer: C) The number of atoms of each element.
Explanation: Subscripts indicate how many atoms of each element are present in a compound.
MCQ 58
Which of the following pairs of substances illustrates the Law of Multiple Proportions?
A) H₂ and O₂
B) CO and CO₂
C) NaCl and KCl
D) CH₄ and C₂H₆
Answer: B) CO and CO₂.
Explanation: Carbon and oxygen combine in different ratios to form carbon monoxide (CO) and carbon dioxide (CO₂).
MCQ 59
How does the Law of Conservation of Mass apply to a closed system?
A) Mass can be created and destroyed.
B) Mass remains unchanged.
C) Mass changes form.
D) Mass can be lost to the environment.
Answer: B) Mass remains unchanged.
Explanation: In a closed system, the total mass of reactants equals the total mass of products, ensuring conservation.
MCQ 60
What is formed when iron reacts with oxygen?
A) Iron sulfate
B) Iron oxide
C) Iron chloride
D) Iron hydroxide
Answer: B) Iron oxide.
Explanation: The reaction of iron with oxygen forms iron oxide, commonly known as rust.
MCQ 61
What is the main focus of stoichiometry in a chemical reaction?
A) Energy changes
B) Mass conservation
C) Reaction rates
D) Physical states
Answer: B) Mass conservation.
Explanation: Stoichiometry primarily focuses on the conservation of mass and the quantitative relationships between reactants and products.
MCQ 62
Which of the following correctly represents a decomposition reaction?
A) H₂ + O₂ → H₂O
B) 2H₂O → 2H₂ + O₂
C) N₂ + 3H₂ → 2NH₃
D) Ca + Cl₂ → CaCl₂
Answer: B) 2H₂O → 2H₂ + O₂.
Explanation: A decomposition reaction involves a single compound breaking down into two or more products.
MCQ 63
In a reaction, if 15 g of substance A produces 10 g of substance B, what is the mass of the leftover substance?
A) 5 g
B) 10 g
C) 15 g
D) 0 g
Answer: A) 5 g.
Explanation: The Law of Conservation of Mass implies that the mass before and after the reaction must equal; if 15 g produces 10 g, then 5 g remains.
MCQ 64
What does the term “molar mass” refer to?
A) The mass of a single atom
B) The mass of one mole of a substance
C) The volume of one mole of gas
D) The total mass of products
Answer: B) The mass of one mole of a substance.
Explanation: Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol).
MCQ 65
Which of the following is NOT a characteristic of a chemical change?
A) Formation of a gas
B) Change in color
C) Change in state
D) Production of light
Answer: C) Change in state.
Explanation: A change in state (like melting or boiling) is a physical change, not necessarily a chemical change.
MCQ 66
What is the purpose of balancing a chemical equation?
A) To show the physical states of compounds
B) To ensure the same number of each type of atom on both sides
C) To represent the energy changes
D) To indicate the temperature of the reaction
Answer: B) To ensure the same number of each type of atom on both sides.
Explanation: Balancing ensures that the law of conservation of mass is followed by having equal numbers of each type of atom in reactants and products.
MCQ 67
Which compound has the smallest mass ratio of elements?
A) CO₂
B) H₂O
C) NH₃
D) CH₄
Answer: B) H₂O.
Explanation: The mass ratio of hydrogen to oxygen in water (1:8) is smaller than in the other compounds listed.
MCQ 68
What happens during a combustion reaction?
A) A compound breaks down into simpler substances.
B) Oxygen reacts with a substance, releasing energy.
C) Two elements combine to form a compound.
D) An acid reacts with a base.
Answer: B) Oxygen reacts with a substance, releasing energy.
Explanation: Combustion reactions typically involve a substance reacting with oxygen to produce heat and light.
MCQ 69
Which law explains the ratio of masses in the formation of compounds?
A) Law of Multiple Proportions
B) Law of Conservation of Mass
C) Law of Definite Proportions
D) Dalton’s Law
Answer: C) Law of Definite Proportions.
Explanation: This law states that a given compound always contains its constituent elements in a fixed mass ratio.
MCQ 70
In an exothermic reaction, what happens to the energy?
A) Energy is absorbed.
B) Energy is released.
C) Energy remains constant.
D) Energy is lost to the environment.
Answer: B) Energy is released.
Explanation: In an exothermic reaction, energy is released to the surroundings, usually in the form of heat.
MCQ 71
Which chemical equation is balanced?
A) H₂ + O₂ → H₂O
B) 2H₂ + O₂ → 2H₂O
C) C + O₂ → CO
D) 2C + O₂ → 2CO
Answer: B) 2H₂ + O₂ → 2H₂O.
Explanation: This equation has equal numbers of each type of atom on both sides, making it balanced.
MCQ 72
What is the primary factor that determines the coefficients in a balanced equation?
A) Temperature
B) Pressure
C) Conservation of mass
D) Reactant concentration
Answer: C) Conservation of mass.
Explanation: Coefficients are determined to ensure that the total mass of reactants equals the total mass of products.
MCQ 73
Which of the following indicates a physical change?
A) Rusting of iron
B) Burning of wood
C) Dissolving salt in water
D) Baking a cake
Answer: C) Dissolving salt in water.
Explanation: Dissolving is a physical change; the salt can be recovered by evaporating the water.
MCQ 74
What does Avogadro’s Law state about equal volumes of gases?
A) They have the same mass.
B) They contain the same number of moles.
C) They have different molecular weights.
D) They are in different states of matter.
Answer: B) They contain the same number of moles.
Explanation: Avogadro’s Law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles.
MCQ 75
When zinc reacts with hydrochloric acid, what is produced?
A) Zinc chloride and hydrogen gas
B) Zinc oxide and water
C) Zinc sulfate and oxygen
D) Zinc hydroxide and chlorine gas
Answer: A) Zinc chloride and hydrogen gas.
Explanation: The reaction of zinc with hydrochloric acid produces zinc chloride (ZnCl₂) and hydrogen gas (H₂).
MCQ 76
In a chemical reaction, what does it mean if a substance is oxidized?
A) It gains electrons.
B) It loses electrons.
C) It gains protons.
D) It loses neutrons.
Answer: B) It loses electrons.
Explanation: Oxidation refers to the loss of electrons during a chemical reaction.
MCQ 77
Which element typically undergoes reduction in a redox reaction?
A) The oxidizing agent
B) The reducing agent
C) The solvent
D) The catalyst
Answer: A) The oxidizing agent.
Explanation: The oxidizing agent gains electrons and is reduced during a redox reaction.
MCQ 78
Which of the following represents a heterogeneous mixture?
A) Saltwater
B) Air
C) Salad
D) Sugar solution
Answer: C) Salad.
Explanation: A salad contains visibly different components, making it a heterogeneous mixture.
MCQ 79
What type of reaction is represented by the equation: 2Na + Cl₂ → 2NaCl?
A) Decomposition
B) Synthesis
C) Combustion
D) Double replacement
Answer: B) Synthesis.
Explanation: This reaction shows two reactants combining to form a single product, NaCl.
MCQ 80
What is the outcome of a double replacement reaction?
A) Reactants form a single product.
B) Atoms are rearranged to form new substances.
C) One element replaces another in a compound.
D) Two compounds exchange ions to form new compounds.
Answer: D) Two compounds exchange ions to form new compounds.
Explanation: In a double replacement reaction, two compounds react and exchange their ions.
MCQ 81
What is the empirical formula for C₃H₆?
A) C₃H₆
B) C₁H₂
C) C₂H₄
D) C₃H₆O
Answer: B) C₁H₂.
Explanation: The empirical formula represents the simplest whole number ratio of atoms, which is C₁H₂ for C₃H₆.
MCQ 82
Which of the following is a product of the combustion of hydrocarbons?
A) Water
B) Carbon dioxide
C) Energy
D) All of the above
Answer: D) All of the above.
Explanation: Combustion of hydrocarbons produces water, carbon dioxide, and releases energy.
MCQ 83
According to the Law of Conservation of Mass, what happens to the mass during a reaction?
A) It is created.
B) It is destroyed.
C) It remains constant.
D) It changes form.
Answer: C) It remains constant.
Explanation: The total mass of reactants equals the total mass of products, thus remaining constant.
MCQ 84
What type of reaction is represented by the equation: 2H₂ + O₂ → 2H₂O?
A) Synthesis
B) Decomposition
C) Combustion
D) Single replacement
Answer: A) Synthesis.
Explanation: This equation shows two reactants combining to form a single product, water.
MCQ 85
What is the mass of 1 mole of any element equal to?
A) The number of protons
B) The atomic weight in grams
C) The density of the element
D) The volume at STP
Answer: B) The atomic weight in grams.
Explanation: The molar mass of an element is numerically equal to its atomic weight expressed in grams.
MCQ 86
Which gas is commonly produced in acid-base reactions?
A) Oxygen
B) Hydrogen
C) Nitrogen
D) Carbon dioxide
Answer: B) Hydrogen.
Explanation: Many acid-base reactions, particularly with metals, produce hydrogen gas as a byproduct.
MCQ 87
Which of the following laws applies to reactions involving mixtures?
A) Law of Definite Proportions
B) Law of Multiple Proportions
C) Law of Conservation of Mass
D) Dalton’s Law
Answer: C) Law of Conservation of Mass.
Explanation: This law applies to mixtures and reactions, stating that mass is conserved in all reactions.
MCQ 88
What is the significance of a balanced equation?
A) It shows energy changes.
B) It represents the types of bonds.
C) It indicates the physical states of reactants.
D) It reflects the conservation of mass.
Answer: D) It reflects the conservation of mass.
Explanation: A balanced equation ensures that the number of atoms for each element is the same on both sides, reflecting mass conservation.
MCQ 89
Which of the following processes is a physical change?
A) Burning wood
B) Dissolving sugar in water
C) Rusting iron
D) Cooking an egg
Answer: B) Dissolving sugar in water.
Explanation: Dissolving sugar in water is a physical change since it can be reversed by evaporation.
MCQ 90
In a redox reaction, what does the reducing agent do?
A) Gains electrons
B) Loses electrons
C) Increases energy
D) Decreases mass
Answer: B) Loses electrons.
Explanation: The reducing agent donates electrons and is oxidized in the process.
MCQ 91
Which law states that all gases at the same temperature and pressure occupy the same volume?
A) Boyle’s Law
B) Charles’s Law
C) Avogadro’s Law
D) Dalton’s Law
Answer: C) Avogadro’s Law.
Explanation: Avogadro’s Law states that equal volumes of gases contain an equal number of molecules at the same temperature and pressure.
MCQ 92
What is produced when an acid reacts with a metal carbonate?
A) Salt and water
B) Salt and hydrogen gas
C) Salt, water, and carbon dioxide
D) Only salt
Answer: C) Salt, water, and carbon dioxide.
Explanation: The reaction produces salt, water, and carbon dioxide gas.
MCQ 93
Which of the following is a characteristic of ionic compounds?
A) They are poor conductors of electricity.
B) They have low melting points.
C) They are soluble in water.
D) They are gaseous at room temperature.
Answer: C) They are soluble in water.
Explanation: Ionic compounds generally dissolve in water and conduct electricity when dissolved.
MCQ 94
What does the term “stoichiometric coefficients” refer to in a balanced equation?
A) The ratios of heat produced
B) The number of moles of each substance
C) The weight of reactants
D) The types of bonds formed
Answer: B) The number of moles of each substance.
Explanation: Stoichiometric coefficients indicate the number of moles of each reactant and product in a balanced equation.
MCQ 95
Which of the following reactions is an example of a single replacement reaction?
A) 2H₂ + O₂ → 2H₂O
B) Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag
C) CaCO₃ → CaO + CO₂
D) NaCl + KBr → NaBr + KCl
Answer: B) Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag.
Explanation: In a single replacement reaction, one element replaces another in a compound.
MCQ 96
In the context of chemical reactions, what does the term “yield” refer to?
A) The temperature at which a reaction occurs
B) The amount of product formed
C) The time taken for a reaction
D) The energy released
Answer: B) The amount of product formed.
Explanation: Yield refers to the quantity of product obtained from a chemical reaction.
MCQ 97
Which of the following is a sign of a chemical change?
A) Change in size
B) Change in shape
C) Change in color
D) Change in state
Answer: C) Change in color.
Explanation: A change in color often indicates a chemical change, whereas size or shape may indicate a physical change.
MCQ 98
What does a catalyst do in a chemical reaction?
A) Increases the mass of reactants
B) Decreases the reaction rate
C) Lowers the activation energy
D) Changes the products formed
Answer: C) Lowers the activation energy.
Explanation: A catalyst speeds up a reaction by lowering the activation energy required for the reaction to proceed.
MCQ 99
In a chemical reaction, if 10 g of reactants produce 8 g of products, what can be inferred?
A) Mass was lost.
B) There was an error in measurement.
C) The reaction was incomplete.
D) Mass is conserved.
Answer: D) Mass is conserved.
Explanation: The law of conservation of mass states that mass cannot be lost in a reaction; the discrepancy might be due to measurement error or gas release.
MCQ 100
What is the molar volume of an ideal gas at standard temperature and pressure (STP)?
A) 22.4 L
B) 24.0 L
C) 18.0 L
D) 30.0 L
Answer: A) 22.4 L.
Explanation: At STP, one mole of an ideal gas occupies 22.4 liters.
MCQ 101
What does the term “limiting reagent” refer to in a chemical reaction?
A) The reactant that is present in excess
B) The reactant that determines the amount of product formed
C) The product that limits the reaction
D) The catalyst used in the reaction
Answer: B) The reactant that determines the amount of product formed.
Explanation: The limiting reagent is the reactant that is completely consumed first, limiting the extent of the reaction.
MCQ 102
What is formed when sodium reacts with water?
A) Sodium hydroxide and hydrogen gas
B) Sodium chloride and oxygen
C) Sodium bicarbonate and water
D) Sodium oxide and hydrogen gas
Answer: A) Sodium hydroxide and hydrogen gas.
Explanation: The reaction of sodium with water produces sodium hydroxide (NaOH) and hydrogen gas (H₂).
MCQ 103
Which of the following laws states that the ratio of the masses of elements in a compound is always the same?
A) Law of Multiple Proportions
B) Law of Definite Proportions
C) Law of Conservation of Mass
D) Dalton’s Law
Answer: B) Law of Definite Proportions.
Explanation: This law asserts that a chemical compound always contains its constituent elements in a fixed mass ratio.
MCQ 104
What happens during a chemical reaction according to the Law of Conservation of Mass?
A) Mass can be created or destroyed.
B) The total mass of reactants equals the total mass of products.
C) Only some elements are conserved.
D) Energy is lost as heat.
Answer: B) The total mass of reactants equals the total mass of products.
Explanation: This law states that in a closed system, mass remains constant during a chemical reaction.
MCQ 105
What type of reaction is represented by the equation: 2H₂ + O₂ → 2H₂O?
A) Single replacement
B) Decomposition
C) Synthesis
D) Double replacement
Answer: C) Synthesis.
Explanation: This reaction shows two reactants (hydrogen and oxygen) combining to form a single product (water).
MCQ 106
Which of the following is an example of a physical change?
A) Iron rusting
B) Water boiling
C) Wood burning
D) Baking a cake
Answer: B) Water boiling.
Explanation: Boiling water is a physical change as it involves a change in state but not a change in chemical composition.
MCQ 107
When balancing a chemical equation, what should be done first?
A) Balance the most complex molecule.
B) Balance the elements present in only one reactant and one product.
C) Balance hydrogen and oxygen last.
D) Use fractions if necessary.
Answer: B) Balance the elements present in only one reactant and one product.
Explanation: It’s usually best to start with elements that appear in only one reactant and one product before moving to others.
MCQ 108
What is the process called when a solid turns directly into a gas?
A) Condensation
B) Sublimation
C) Evaporation
D) Freezing
Answer: B) Sublimation.
Explanation: Sublimation is the process where a solid changes directly into a gas without passing through a liquid state.
MCQ 109
What does the term “aqueous solution” refer to?
A) A solution containing gas
B) A solution in which water is the solvent
C) A solution containing solid particles
D) A solution that conducts electricity
Answer: B) A solution in which water is the solvent.
Explanation: An aqueous solution is one in which water is used as the solvent for dissolving substances.
MCQ 110
Which of the following compounds is formed through ionic bonding?
A) CO₂
B) H₂O
C) NaCl
D) CH₄
Answer: C) NaCl.
Explanation: Sodium chloride (NaCl) is formed through ionic bonding between sodium (Na) and chlorine (Cl) ions.
MCQ 111
What does the term “activation energy” refer to?
A) The energy released during a reaction
B) The energy needed to start a reaction
C) The energy available after a reaction
D) The energy lost to the environment
Answer: B) The energy needed to start a reaction.
Explanation: Activation energy is the minimum energy required to initiate a chemical reaction.
MCQ 112
What is the main characteristic of exothermic reactions?
A) They absorb energy.
B) They release energy.
C) They require constant heat.
D) They do not involve energy changes.
Answer: B) They release energy.
Explanation: Exothermic reactions release energy in the form of heat or light to the surroundings.
MCQ 113
Which law describes the behavior of gases under varying pressures and temperatures?
A) Charles’s Law
B) Boyle’s Law
C) Ideal Gas Law
D) Avogadro’s Law
Answer: C) Ideal Gas Law.
Explanation: The Ideal Gas Law (PV = nRT) relates pressure (P), volume (V), temperature (T), and the amount of gas (n).
MCQ 114
Which of the following describes a double replacement reaction?
A) A + B → C
B) A + BC → AC + B
C) AB + CD → AD + CB
D) A → B + C
Answer: C) AB + CD → AD + CB.
Explanation: In a double replacement reaction, two compounds exchange ions to form two new compounds.
MCQ 115
What is produced during the electrolysis of water?
A) Oxygen and hydrogen gases
B) Carbon dioxide and water
C) Sodium and chloride
D) Nitrogen and ammonia
Answer: A) Oxygen and hydrogen gases.
Explanation: Electrolysis of water splits it into hydrogen gas and oxygen gas.
MCQ 116
What happens to the temperature of a substance during a phase change?
A) It increases steadily.
B) It decreases steadily.
C) It remains constant.
D) It fluctuates wildly.
Answer: C) It remains constant.
Explanation: During a phase change, the temperature of a substance remains constant while energy is added or removed.
MCQ 117
What is the primary product of the combustion of fossil fuels?
A) Methane
B) Water
C) Carbon monoxide
D) Carbon dioxide
Answer: D) Carbon dioxide.
Explanation: The combustion of fossil fuels primarily produces carbon dioxide (CO₂) along with water (H₂O) and energy.
MCQ 118
What is a characteristic of metallic bonding?
A) Electrons are transferred between atoms.
B) Electrons are shared between specific atoms.
C) Electrons are delocalized and shared among many atoms.
D) Electrons are fixed in place.
Answer: C) Electrons are delocalized and shared among many atoms.
Explanation: In metallic bonding, electrons are free to move throughout the structure, contributing to conductivity.
MCQ 119
In a chemical reaction, which of the following represents the reactants?
A) The products formed after the reaction
B) The starting materials that undergo change
C) The energy released
D) The catalyst used in the reaction
Answer: B) The starting materials that undergo change.
Explanation: Reactants are the substances that undergo change during a chemical reaction to form products.
MCQ 120
Which type of reaction occurs when an acid reacts with a base?
A) Synthesis
B) Decomposition
C) Neutralization
D) Redox
Answer: C) Neutralization.
Explanation: A neutralization reaction occurs when an acid reacts with a base to produce water and a salt.
MCQ 121
What is the byproduct of the reaction between an acid and a metal?
A) Water
B) Salt
C) Oxygen
D) Carbon dioxide
Answer: B) Salt.
Explanation: The reaction between an acid and a metal typically produces a salt and hydrogen gas.
MCQ 122
What does the term “molarity” refer to?
A) The volume of a solution
B) The amount of solute per liter of solution
C) The mass of solute in grams
D) The concentration of a gas
Answer: B) The amount of solute per liter of solution.
Explanation: Molarity is defined as the number of moles of solute divided by the volume of solution in liters.
MCQ 123
Which of the following is an indicator of a chemical change?
A) Change in temperature
B) Change in shape
C) Change in mass
D) Change in size
Answer: A) Change in temperature.
Explanation: A change in temperature can indicate that a chemical reaction has occurred, especially if it releases or absorbs heat.
MCQ 124
What is the main characteristic of a chemical equation?
A) It only shows reactants.
B) It must be balanced.
C) It can be written in any order.
D) It ignores states of matter.
Answer: B) It must be balanced.
Explanation: A chemical equation must be balanced to satisfy the Law of Conservation of Mass.
MCQ 125
Which of the following gases is produced during the reaction of vinegar with baking soda?
A) Hydrogen
B) Oxygen
C) Carbon dioxide
D) Nitrogen
Answer: C) Carbon dioxide.
Explanation: The reaction of vinegar (acetic acid) with baking soda (sodium bicarbonate) produces carbon dioxide gas.
MCQ 126
What is the function of a catalyst in a chemical reaction?
A) To change the reaction products
B) To increase the activation energy
C) To speed up the reaction without being consumed
D) To slow down the reaction
Answer: C) To speed up the reaction without being consumed.
Explanation: A catalyst increases the rate of a reaction by lowering the activation energy and is not consumed in the process.
MCQ 127
In which type of reaction does one element replace another in a compound?
A) Synthesis
B) Double replacement
C) Decomposition
D) Single replacement
Answer: D) Single replacement.
Explanation: In a single replacement reaction, one element replaces another in a compound.
MCQ 128
What does a neutral pH of 7 indicate?
A) Basic solution
B) Acidic solution
C) Neither acidic nor basic
D) Very acidic
Answer: C) Neither acidic nor basic.
Explanation: A pH of 7 indicates a neutral solution, meaning it is neither acidic nor basic.
MCQ 129
Which of the following represents a decomposition reaction?
A) 2H₂ + O₂ → 2H₂O
B) 2NaCl → 2Na + Cl₂
C) NH₃ + HCl → NH₄Cl
D) C + O₂ → CO₂
Answer: B) 2NaCl → 2Na + Cl₂.
Explanation: A decomposition reaction involves a single compound breaking down into two or more simpler products.
MCQ 130
What is produced when an alkali metal reacts with water?
A) Metal oxide
B) Salt and hydrogen
C) Acid
D) Hydroxide and hydrogen
Answer: D) Hydroxide and hydrogen.
Explanation: The reaction of alkali metals with water produces metal hydroxides and hydrogen gas.
MCQ 131
Which of the following elements is a diatomic molecule?
A) Carbon
B) Oxygen
C) Helium
D) Argon
Answer: B) Oxygen.
Explanation: Diatomic molecules consist of two atoms; oxygen (O₂) is one such example.
MCQ 132
What is the primary role of a solvent in a solution?
A) To change the chemical properties
B) To dissolve the solute
C) To create a solid
D) To increase temperature
Answer: B) To dissolve the solute.
Explanation: The solvent is the substance that dissolves the solute to form a solution.
MCQ 133
What does the term “analyte” refer to in chemistry?
A) The substance being analyzed
B) The solvent in a reaction
C) The catalyst used
D) The resulting product
Answer: A) The substance being analyzed.
Explanation: An analyte is the specific substance whose chemical constituents are being identified and measured.
MCQ 134
Which of the following compounds has the highest melting point?
A) NaCl
B) CO₂
C) H₂O
D) CH₄
Answer: A) NaCl.
Explanation: Sodium chloride (NaCl) has a high melting point due to its strong ionic bonds.
MCQ 135
What type of reaction occurs when two or more substances combine to form a single product?
A) Decomposition
B) Single replacement
C) Synthesis
D) Combustion
Answer: C) Synthesis.
Explanation: A synthesis reaction involves the combination of two or more reactants to produce one product.
MCQ 136
What is the effect of increasing the concentration of reactants in a chemical reaction?
A) Decreases the rate of reaction
B) Has no effect
C) Increases the rate of reaction
D) Makes the reaction exothermic
Answer: C) Increases the rate of reaction.
Explanation: Increasing the concentration of reactants typically increases the rate of reaction due to more frequent collisions.
MCQ 137
What is the primary gas produced during the fermentation of sugars?
A) Oxygen
B) Nitrogen
C) Carbon dioxide
D) Hydrogen
Answer: C) Carbon dioxide.
Explanation: Fermentation of sugars by yeast produces carbon dioxide and alcohol as byproducts.
MCQ 138
Which of the following compounds is considered a strong acid?
A) Acetic acid
B) Citric acid
C) Hydrochloric acid
D) Carbonic acid
Answer: C) Hydrochloric acid.
Explanation: Hydrochloric acid (HCl) is a strong acid that completely dissociates in water.
MCQ 139
What is formed when an acid reacts with a metal?
A) Water and carbon dioxide
B) Salt and hydrogen gas
C) Salt and oxygen gas
D) Water and salt
Answer: B) Salt and hydrogen gas.
Explanation: The reaction between an acid and a metal typically produces a salt and hydrogen gas.
MCQ 140
What does the term “endothermic reaction” refer to?
A) A reaction that releases energy
B) A reaction that absorbs energy
C) A reaction that has no energy change
D) A reaction that occurs spontaneously
Answer: B) A reaction that absorbs energy.
Explanation: An endothermic reaction requires an input of energy, typically in the form of heat.
MCQ 141
Which of the following represents a combination reaction?
A) 2H₂ + O₂ → 2H₂O
B) 2NaCl → 2Na + Cl₂
C) H₂O → H₂ + O₂
D) CH₄ + O₂ → CO₂ + H₂O
Answer: A) 2H₂ + O₂ → 2H₂O.
Explanation: A combination reaction occurs when two or more reactants combine to form a single product.
MCQ 142
What is the primary characteristic of a chemical bond?
A) It is a physical interaction.
B) It involves the sharing or transfer of electrons.
C) It only occurs in solids.
D) It cannot be broken.
Answer: B) It involves the sharing or transfer of electrons.
Explanation: Chemical bonds are formed by the sharing (covalent bonds) or transfer (ionic bonds) of electrons between atoms.
MCQ 143
Which of the following is NOT a characteristic of acids?
A) Sour taste
B) pH less than 7
C) Slippery feel
D) Turns blue litmus red
Answer: C) Slippery feel.
Explanation: A slippery feel is characteristic of bases, not acids.
MCQ 144
What type of reaction is represented by the equation: CaCO₃ → CaO + CO₂?
A) Synthesis
B) Decomposition
C) Single replacement
D) Double replacement
Answer: B) Decomposition.
Explanation: This reaction shows a single compound breaking down into two or more products, characteristic of decomposition reactions.
MCQ 145
Which of the following statements is true according to Dalton’s atomic theory?
A) Atoms can be created and destroyed.
B) All atoms of a given element are identical in mass and properties.
C) Atoms can be divided into smaller particles.
D) Different elements can combine in any ratio.
Answer: B) All atoms of a given element are identical in mass and properties.
Explanation: Dalton’s atomic theory states that atoms of the same element are identical in mass and properties.
MCQ 146
What is the main product when glucose undergoes complete combustion?
A) Water and carbon dioxide
B) Water and carbon monoxide
C) Ethanol and carbon dioxide
D) Hydrogen and oxygen
Answer: A) Water and carbon dioxide.
Explanation: The complete combustion of glucose produces water (H₂O) and carbon dioxide (CO₂).
MCQ 147
Which of the following represents an oxidation reaction?
A) 2H₂ + O₂ → 2H₂O
B) C + O₂ → CO₂
C) Zn + Cu²⁺ → Zn²⁺ + Cu
D) Fe²⁺ → Fe³⁺
Answer: D) Fe²⁺ → Fe³⁺.
Explanation: Oxidation is the loss of electrons; here, iron is losing an electron and increasing its oxidation state.
MCQ 148
Which gas is typically produced when a carbonate reacts with an acid?
A) Oxygen
B) Carbon dioxide
C) Hydrogen
D) Nitrogen
Answer: B) Carbon dioxide.
Explanation: The reaction of carbonates with acids produces carbon dioxide gas as one of the products.
MCQ 149
Which law states that when gases combine or are produced in a chemical reaction, they do so in simple whole number ratios by volume?
A) Dalton’s Law
B) Avogadro’s Law
C) Boyle’s Law
D) Charles’s Law
Answer: B) Avogadro’s Law.
Explanation: Avogadro’s Law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
MCQ 150
What does a balanced chemical equation indicate?
A) The reaction is complete.
B) The relative amounts of reactants and products involved.
C) The type of bonds formed.
D) The energy changes involved.
Answer: B) The relative amounts of reactants and products involved.
Explanation: A balanced equation shows the ratio of reactants to products, reflecting the conservation of mass.
MCQ 151
What happens to the pressure of a gas when its volume decreases at constant temperature?
A) It increases.
B) It decreases.
C) It remains constant.
D) It fluctuates.
Answer: A) It increases.
Explanation: According to Boyle’s Law, pressure increases when volume decreases if temperature is held constant.
MCQ 152
What does the term “solubility” refer to?
A) The amount of solute that can dissolve in a solvent
B) The state of matter of a solution
C) The temperature at which a solute dissolves
D) The pressure required for a solute to dissolve
Answer: A) The amount of solute that can dissolve in a solvent.
Explanation: Solubility is the measure of how much solute can dissolve in a specific amount of solvent at a given temperature.
MCQ 153
What occurs during a redox reaction?
A) No electrons are transferred.
B) Only oxidation occurs.
C) Reduction and oxidation occur simultaneously.
D) Only reduction occurs.
Answer: C) Reduction and oxidation occur simultaneously.
Explanation: In a redox reaction, one substance is oxidized (loses electrons) and another is reduced (gains electrons) at the same time.
MCQ 154
Which of the following statements is true regarding exothermic reactions?
A) They absorb heat.
B) They feel cold to the touch.
C) They release heat.
D) They have a positive change in enthalpy.
Answer: C) They release heat.
Explanation: Exothermic reactions release energy, usually in the form of heat, to the surroundings.
MCQ 155
What is formed when an acid reacts with a base?
A) Salt and water
B) Hydrogen gas
C) Carbon dioxide
D) Oxygen gas
Answer: A) Salt and water.
Explanation: The reaction between an acid and a base typically produces a salt and water, known as a neutralization reaction.
MCQ 156
Which of the following is a characteristic of bases?
A) Sour taste
B) Turns red litmus blue
C) Produces H⁺ ions in solution
D) Feels oily
Answer: B) Turns red litmus blue.
Explanation: Bases turn red litmus paper blue and have a bitter taste.
MCQ 157
What is the outcome of a complete combustion reaction?
A) Water and oxygen
B) Water and carbon monoxide
C) Water and carbon dioxide
D) Water and heat only
Answer: C) Water and carbon dioxide.
Explanation: Complete combustion of hydrocarbons results in the production of water (H₂O) and carbon dioxide (CO₂).
MCQ 158
What is the main characteristic of ionic compounds?
A) They have low melting points.
B) They conduct electricity in solid form.
C) They are soluble in non-polar solvents.
D) They form crystals.
Answer: D) They form crystals.
Explanation: Ionic compounds typically form crystal lattices, which contribute to their high melting points and solubility in water.
MCQ 159
Which of the following reactions is an example of a synthesis reaction?
A) 2H₂ + O₂ → 2H₂O
B) CaCO₃ → CaO + CO₂
C) 2Na + Cl₂ → 2NaCl
D) H₂O → H₂ + O₂
Answer: C) 2Na + Cl₂ → 2NaCl.
Explanation: A synthesis reaction involves two or more reactants combining to form a single product.
MCQ 160
What happens during a phase transition from liquid to gas?
A) Energy is released.
B) Energy is absorbed.
C) No energy change occurs.
D) The substance loses mass.
Answer: B) Energy is absorbed.
Explanation: The phase transition from liquid to gas (evaporation) requires energy absorption from the surroundings
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