Question:medium

On electrolysis of very dilute aqueous solution of NaCl using platinum electrodes :

Show Hint

Dilute brine → water oxidised at anode → O2 (Cl2 needs concentrated NaCl); H2 forms at cathode.
Updated On: Jun 15, 2026
  • H2 gas is evolved at anode.
  • Na is produced at anode.
  • O2 gas is evolved at anode.
  • H2 gas is evolved at cathode.
Show Solution

The Correct Option is C

Solution and Explanation

Compare the anode candidates for dilute brine. Oxidising Cl to Cl2 requires a reasonable chloride concentration; in a $very$ $dilute$ solution that route is suppressed, so water is oxidised instead, releasing O2 at the anode:
\[2H_2O \rightarrow O_2 + 4H^+ + 4e^-\]Sodium is never deposited from aqueous solution and no gas is reduced at the anode, ruling out the other anode options. The condition-specific answer is (C), O2 at the anode (H2 is simultaneously released at the cathode).
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