In which one of the following, one Faraday of
electricity will liberate 1/2 mole of the metal-
(A) AuCl3 (B) FeCl3 (C) CuSO4 (D) NaCl

Please mention the reason.

Dear student,
Faraday's laws of electrolysis relate the amount of liberated mass at an electrode to the quantity of electricity passing through the electrode. Faraday's first law states that the amount of current passed through an electrode is directly proportional to the amount of material liberated from it.
W=EIt/96500
1 valency=1faraday=1 mole of electrone charge
so, in option (a) $A{l}^{+3}$ it has +3 valency so it consume 1/3 faraday
option (b) $F{e}^{+3}$ it has also +3 valency so it consume 1/3 faraday
option (c) $C{u}^{+2}$ it has +2 valency  so it comsume 1/2 faraday
option (d) $N{a}^{+}$ it has +1 valency so it consume 1 faraday
so option (c) is the right answer 
Regards