Here is a $ 0.050 \; M $ solution of the weak base pyridine $(C_5H_5N$ , $K_b$ $=$ $1.7\cdot 10^{-4})$
$C_5H_5N$ $ +$ $H_2O$ 
$HC_5H_5N^+$ $+$ $OH^-$
What are the initial molarities of each species ?
a) $0.050\;M$, $0\;M$, $0\;M$ b) $0\;M$, $0.050\;M$, $0\;M$ c) $0.050\;M$, $0.050\;M$, $0.050\;M$ d) $0.050\;M$, $0.050\;M$, $0\;M$
Answer: a) $0.050\;M$, $0\;M$, $0\;M$