When electric current is passed through acidified water, 448 mL of hydrogen gas at STP is collected at the cathode in 965 seconds. The current passed in amperes is :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4.0
By Faraday’s first law, the amount of substance set free at an electrode is proportional to the charge passed. At the cathode \( \ce{2H+ + 2e- -> H2} \), so 1 mol \( \ce{H2} \) needs 2 mol of electrons (2 F).
\( \displaystyle n(\ce{H2}) = \frac{448\ \text{mL}}{22400\ \text{mL mol}^{-1}} = 0.02\ \text{mol} \)
Moles of electrons = 2 × 0.02 = 0.04 mol
\( Q = 0.04 \times 96500\ \text{C} = 3860\ \text{C} \)
\( \displaystyle I = \frac{Q}{t} = \frac{3860\ \text{C}}{965\ \text{s}} = 4.0\ \text{A} \)
NCERT (2026-27 edition):
Faraday’s Laws of Electrolysis – “… (i) First Law: The amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte (solution or melt).”