Q1. [1] § 1.1 CHEMICAL EQUATIONS § 1.1.1 Writing a Chemical Equation
Electrolysis of water is a decomposition reaction. The mass ratio (MH : MO) of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is :
- (A) 8 : 1
- (B) 2 : 1
- (C) 1 : 2
- (D) 1 : 8
Previously asked in CBSE board exam
2025 31/1/1 Q1
Generated by claude-sonnet-4-6 · 2026-06-14 10:31 · grounding rag
Model Answer
(D) 1 : 8
The balanced equation is 2H₂O → 2H₂ + O₂. Mass of H₂ = 4 g, mass of O₂ = 32 g, so M_H : M_O = 4 : 32 = 1 : 8.
Explanation
The question asks for the mass ratio, not the mole or volume ratio. From the balanced equation, 2 moles of H₂O give 2 moles of H₂ (mass = 4 g) and 1 mole of O₂ (mass = 32 g). So the mass ratio is 1 : 8. A common mistake is to pick 1 : 2 (mole ratio) instead of the mass ratio.
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