How many moles of electrons are needed to deposit 0.2 mol of copper from Cu²⁺? Assume a suitable molten electrolyte and 100% current efficiency.

A) 0.8 mol e⁻

B) 0.2 mol e⁻

C) 1.4 mol e⁻

D) 0.4 mol e⁻

Answer: D

Explanation: Each Cu²⁺ ion requires 2 electron(s) to form one metal atom. 0.2 mol metal therefore needs 0.2 × 2 = 0.4 mol electrons.