The correct options are
A Au
C Cu
D Ag
Ag (silver),Au (gold),Cu (copper) can be obtained by electrolysis of the aqueous solution of their salts.but Mg(magnesium) cannot be obtained by electrolysis of the aqueous solution of their salts,because as Mg is more electropositive in nature it can reacts with OH ions in the water and can form Mg(OH)2.
Hence options A,B & C are correct.