Oxidation as loss of electrons at the anode

Steps:

• Define oxidation as the loss of electrons from a species.
• In electrolysis, oxidation occurs at the anode where anions lose electrons.
• Examine options for electron loss producing a visible change.
• Select the option matching anodic oxidation with a color observation.

Why C is correct:

• In NaCl electrolysis, Cl⁻ ions oxidize at the anode (2Cl⁻ → Cl₂ + 2e⁻), producing green chlorine gas, directly observing electron loss.

Why the others are wrong:

• A: Heating CuSO₄·5H₂O to anhydrous CuSO₄ is dehydration, not electron loss.
• B: Cu²⁺ gaining electrons at the cathode (Cu²⁺ + 2e⁻ → Cu) is reduction, not oxidation.
• D: Ag⁺ + Cl⁻ → AgCl is precipitation via ion combination, not electron transfer.

Final answer: C