In an electrolytic cell, a current of 2.0 A is passed through a solution of copper(II) sulphate for 1 hour 4 minutes and 20 seconds. What mass of copper is deposited at the cathode? [Cu = 64, F = 96500 C mol⁻¹]

Time = 1 hr 4 min 20 s = 3600 + 240 + 20 = 3860 s. Charge Q = I × t = 2.0 × 3860 = 7720 C. Moles of electrons = 7720 ÷ 96500 = 0.08 mol. Since Cu²⁺ + 2e⁻ → Cu, moles of Cu = 0.08 ÷ 2 = 0.04 mol. Mass of Cu = 0.04 × 64 = 2.56 g. Option A results from forgetting to divide by 2 for the 2-electron transfer, while C and D are other plausible arithmetic errors.