Electrolysis of aqueous CuSO4 with copper electrodes

Steps:

• At cathode (reduction): Cu²⁺ + 2e⁻ → Cu, depositing copper so cathode mass increases.
• At anode (oxidation): Cu → Cu²⁺ + 2e⁻, dissolving copper so anode mass decreases.
• Cu²⁺ ions from anode replace those reduced at cathode, keeping solution concentration constant.
• Blue color from Cu²⁺(aq) thus stays the same.

Why D is correct:

• Matches anode mass decrease, cathode mass increase, and unchanged color due to balanced Cu²⁺ production and consumption.

Why the others are wrong:

• A: Anode mass decreases, does not increase.
• B: Anode mass decreases (not increases); color stays blue, does not pale.
• C: Color stays the same, does not become paler.

Final answer: D