An amount of $0.15$ mole of pyridinium chloride has been added into $500 \mathrm{ml}$ of 0.2 M pyridine solution. Calculate pH and hydroxyl ion concentration in the resulting solution assuming no change in volume. $K_{\mathrm{b}}$ for pyridine $=1.5 \times 10^{-9}$. $(\log 2=0.3, \log 0.3=0.48)$
(a) $9.0$
(b) $5.0$
(c) $8.64$
(d) $5.36$