The time period to coat a metal surface of 80 cm2 with 5 × 10–3 cm thick layer of silver (density 1.05 g cm–3) with the passage of 3A current through a silver nitrate solution is

mass of Ag  required to coat the given surface = d×thickness×surface Area=80×5×10-3×1.05=0.42gmNumber of equivalents of Ag = 0.42108Number of coulombs required =96500×0.42108=375.28 CoulAmp×sec=coulomb t (sec) =375.283≅125