The hydrogen ion concentration of a 10-8 M HCl aqueous solution at 298 K(Kw 10-14)is:
(b) In aqueous solution of 10-8 M HCl, [H+] is based upon the concentration of H+ ion of water 10-8 M HCl and concentration of H+ ion of water Kw of H2O=10-14=[H+][OH-] or[H+]=10-7 M (due to its neutral behaviour)
So, in aqueous solution of 10-8 M HCI,
Hence, answer is nearer to (b).