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During electrolysis of sulphuric acid, the following processes are possible at cathode:

1. 2H2O(l) -> O2(g) + 4H+(aq) + 4e-, E° = +1.23 V
2. 2SO4^2-(aq) -> S2O8^2-(aq) + 2e-, E° = +1.96 V
3. For dilute sulphuric acid, first reaction is preferred but for concentrated acid, second reaction is preferred.
4. None of the above

Correct answer: For dilute sulphuric acid, first reaction is preferred but for concentrated acid, second reaction is preferred.

Solution

In dilute sulphuric acid, water oxidation (reaction A) occurs due to its lower electrode potential. In concentrated acid, the higher concentration of sulfate ions favors reaction B despite its higher potential.

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