c
In aqueous solution of \(10^{-8} M H C l,\left[H^{+}\right]\) is based upon the concentration of \(H^{+}\) ion of \(10^{-8} M H C l\) and concentration of \(H^{+}\) ion of water.

\(K_{w} \text { of } H_{2} O=10^{-14}=\left[H^{+}\right]\left[O H^{-}\right]\)

or \(\left[H^{+}\right]=10^{-7} M\) (due to its neutral behaviour)

So, in aqueous solution of \(10^{-8} \mathrm{MHCl}\)

\(\left[H^{+}\right] =\left[H^{+}\right] \text {of } \mathrm{HCl}+\left[H^{+}\right] \text {of water }\)

\(=10^{-8}+10^{-7}\)

\(=11 \times 10^{-8} M \approx 1.10 \times 10^{-7} M\)