Q11. The reaction between zinc and dilute hydrochloric acid produces hydrogen. Which role does zinc play in this reaction?
A) Reducing agent
B) Oxidizing agent
C) Catalyst
D) Neutral compound
Answer: A) Reducing agent
Explanation: In the reaction between zinc and dilute HCl, zinc donates electrons to hydrogen ions, reducing them to hydrogen gas. Hence, zinc acts as a reducing agent.
Q12. The atomic number of hydrogen is 1. What does this indicate about its atomic structure?
A) One proton and no neutron
B) One proton and one neutron
C) One neutron and one electron
D) Two protons and one electron
Answer: A) One proton and no neutron
Explanation: The atomic number of hydrogen is 1, which means it has one proton and no neutrons in its most common isotope, protium (¹H).
Q13. Which of the following metals produces hydrogen gas when reacted with steam?
A) Sodium
B) Magnesium
C) Potassium
D) Lithium
Answer: B) Magnesium
Explanation: Magnesium reacts with steam to form magnesium oxide and hydrogen gas. Sodium and potassium react violently with cold water, while lithium reacts slowly with water.
Q14. Which property of hydrogen makes it useful as a fuel?
A) High atomic mass
B) Non-flammability
C) High calorific value
D) High density
Answer: C) High calorific value
Explanation: Hydrogen has the highest calorific value among known fuels, making it an excellent energy source when burned.
Q15. Hydrogen peroxide (H₂O₂) is a good example of hydrogen acting as:
A) An oxidizing agent
B) A reducing agent
C) Both A and B
D) Neither A nor B
Answer: C) Both A and B
Explanation: Hydrogen peroxide can act both as an oxidizing agent (e.g., in the presence of reducing substances) and as a reducing agent (e.g., in the presence of strong oxidizers like potassium permanganate).
Q16. Which of the following statements about hydrogen is true?
A) Hydrogen can act only as a reducing agent.
B) Hydrogen always exists as a diatomic molecule.
C) Hydrogen is the heaviest element.
D) Hydrogen has three naturally occurring isotopes.
Answer: D) Hydrogen has three naturally occurring isotopes.
Explanation: Hydrogen has three isotopes: protium (¹H), deuterium (²H), and tritium (³H). It can act as both a reducing and oxidizing agent, and it’s the lightest element, not the heaviest.
Q17. In which of the following reactions does hydrogen act as an oxidizing agent?
A) H₂ + Cl₂ → 2HCl
B) H₂ + O₂ → 2H₂O
C) H₂ + C → CH₄
D) H₂ + Na → NaH
Answer: D) H₂ + Na → NaH
Explanation: In this reaction, hydrogen accepts an electron from sodium, thus acting as an oxidizing agent.
Q18. What is the oxidation state of hydrogen in H₂O₂ (hydrogen peroxide)?
A) +1
B) -1
C) 0
D) -2
Answer: A) +1
Explanation: In hydrogen peroxide (H₂O₂), hydrogen has an oxidation state of +1, while oxygen has an oxidation state of -1.
Q19. Which of the following reactions is used to prepare heavy water (D₂O)?
A) Electrolysis of ordinary water
B) Reaction of hydrogen with oxygen
C) Reaction of deuterium with oxygen
D) None of the above
Answer: A) Electrolysis of ordinary water
Explanation: Heavy water (D₂O) is prepared by the electrolysis of ordinary water, where deuterium gets concentrated in the residual water as hydrogen escapes.
Q20. Which of the following compounds contains hydrogen in the negative oxidation state?
A) NH₃
B) H₂S
C) NaH
D) HCl
Answer: C) NaH
Explanation: In sodium hydride (NaH), hydrogen has an oxidation state of -1, as it gains an electron from sodium.
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