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In electrolysis of NaCl, when Pt electrode is taken, then H2 is liberated at cathode while with Hg cathode, it forms sodium amalgam. This is because

1. Hg is more inert than Pt
2. More voltage is required to reduce H⁺ at Hg than at Pt
3. Na is dissolved in Hg while it does not dissolve in Pt
4. Conc. of H⁺ ions is larger when Pt electrode is taken

Correct answer: Na is dissolved in Hg while it does not dissolve in Pt

Solution

Sodium forms an amalgam with mercury because it dissolves in Hg, whereas it does not dissolve in Pt. This difference in behavior explains the observed products during electrolysis.

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