Q31. Which of the following is not a correct method for preparing hydrogen in the laboratory?
A) Reaction of metals with acids
B) Reaction of alkali metals with cold water
C) Electrolysis of brine
D) Heating sodium with potassium
Answer: D) Heating sodium with potassium
Explanation: Heating sodium with potassium is not a method to prepare hydrogen. Hydrogen is commonly prepared by reacting metals with acids or electrolysis of brine.
Q32. Hydrogen is placed in the reactivity series:
A) Above sodium
B) Below iron
C) Between copper and lead
D) Between zinc and copper
Answer: D) Between zinc and copper
Explanation: In the reactivity series, hydrogen is placed between zinc and copper, meaning it is less reactive than zinc but more reactive than copper.
Q33. Which of the following pairs of elements does not form a hydride?
A) Sodium and hydrogen
B) Fluorine and hydrogen
C) Carbon and hydrogen
D) Helium and hydrogen
Answer: D) Helium and hydrogen
Explanation: Helium is a noble gas and does not form hydrides with hydrogen due to its inert nature.
Q34. Which property of hydrogen allows it to be used in the hydrogenation of oils?
A) Oxidizing nature
B) Reducing nature
C) High solubility in water
D) Inertness
Answer: B) Reducing nature
Explanation: Hydrogen acts as a reducing agent in the hydrogenation of unsaturated oils, converting them into saturated fats.
Q35. Hydrogen is used in fuel cells because:
A) It is easily available
B) It is a good reducing agent
C) It has high energy content
D) It produces carbon dioxide as a byproduct
Answer: C) It has high energy content
Explanation: Hydrogen has a high energy content and when used in fuel cells, it produces electricity with water as the only byproduct, making it a clean energy source.
Q36. The catalytic reduction of alkynes to alkenes using hydrogen is called:
A) Sabatier process
B) Wurtz reaction
C) Lindlar reduction
D) Friedel-Crafts reaction
Answer: C) Lindlar reduction
Explanation: Lindlar reduction involves the catalytic hydrogenation of alkynes to alkenes, using a poisoned catalyst to stop further reduction to alkanes.
Q37. Which of the following is not an isotope of hydrogen?
A) Protium
B) Deuterium
C) Tritium
D) Hydronium
Answer: D) Hydronium
Explanation: Hydronium (H₃O⁺) is not an isotope but rather a hydrated proton. Protium, deuterium, and tritium are the isotopes of hydrogen.
Q38. Hydrogen reacts explosively with which of the following elements?
A) Oxygen
B) Nitrogen
C) Fluorine
D) Neon
Answer: C) Fluorine
Explanation: Hydrogen reacts explosively with fluorine, forming hydrogen fluoride (HF), due to the highly reactive nature of fluorine.
Q39. Hydrogen is used in weather balloons because:
A) It is non-flammable
B) It is lighter than air
C) It is a good conductor of electricity
D) It dissolves in air
Answer: B) It is lighter than air
Explanation: Hydrogen is much lighter than air, which allows weather balloons filled with hydrogen to rise to great altitudes.
Q40. Hydrogen shows similarity in its chemical properties with which of the following groups?
A) Group 1 (alkali metals)
B) Group 2 (alkaline earth metals)
C) Group 16 (chalcogens)
D) Group 17 (halogens)
Answer: D) Group 17 (halogens)
Explanation: Hydrogen shows similarity to Group 17 elements (halogens) in its ability to form diatomic molecules (H₂ like Cl₂) and its tendency to gain one electron to form H⁻, like halogens forming X⁻ ions.
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