When $0.1\; mol$ of $CH_3NH_2$ (ionisation constant, $K_b = 5 \times 10^{-4}$) is mixed with $0.08\;mol\; HCl$ and the volume is made up to $1\; L$ find the [$H^+$] of resulting solution,

Question

(a) $8 \times 10^{-2}$

(b) $2 \times 10^{-11}$

(c) $1.23 \times 10^{-4}$

(d) $8 \times 10^{-11}$