Electrolysis products yielding colourless gases at both electrodes

Steps:

• Recall electrode reactions: cathode reduces to H2 from water or metal; anode oxidizes anion to gas or O2 from water.
• For aqueous solutions, prioritize water discharge if anion is not easily oxidized.
• Identify gases: H2 (colourless) at cathode, O2 (colourless) or halogen (coloured) at anode.
• Select electrolyte where both electrodes produce H2 and O2.

Why C is correct:

• Dilute H2SO4 undergoes water electrolysis: 2H2O → 2H2 (cathode) + O2 (anode), both colourless gases per Faraday's laws.

Why the others are wrong:

• A: Cu2+ reduced to pink Cu metal at cathode, not gas.
• B: Cl- oxidized to greenish-yellow Cl2 gas at anode.
• D: Pb2+ reduced to molten Pb metal at cathode; Br- oxidized to brown Br2 gas at anode.

Final answer: C