The electrolysis of a solution resulted in the formation of H2(g) at the cathode and O2(g) at the anode. The solution is :
AgCl(aq)
H2SO4(aq)
highly concentrated Nacl(aq) solution
CuCl2(aq)
In electrolysis of concentrated CI-, Cl2(g) is evolved in place of O2(g).