(a)
$NH_{4}OH \rightleftharpoons NH_{4}^{+} + OH^{-}$
At $t = 00.1\ \ \ \ \ \ M\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0\ \ \ \ \ \ \ \ \ \ 0$
At equilibrium $\left( 0.1 - \frac{1.3 \times 0.1}{100}M \right)\ \ 0.0013\ M(0.0013\ M)$
$= 0.1\$M
$= \left\lbrack OH^{-} \right\rbrack = 0.0013\ M = 13 \times 10^{- 4}$ M
$pOH = - \log{\left\lbrack OH^{-} \right\rbrack\text{=} - \log{\left( 13 \times 10^{- 4} \right) = 2.89}}$
$pH = 14 - 2.89 = 11.11$