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.
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