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 changes in molarity of each species ?
a) +x M, -x M, -x M b) -x M, -x M, +x M c) -x M, -x M, -x M d) -x M, +x M, +x M
Answer: d) -x M, +x M, +x M