Answer
$0.1M$ $H_2S$ is more acidic.
Work Step by Step
** You can find the $K_a$ values on table: 14.2 (Page 624)
Since both solutions have the same concentration, we just have to determine which compound is more acidic:
-$H_2S$:
$H_2S$ is an acid with $K_a = 1 \times 10^{-7}$
-$HCN$:
$HCN$ is an acid with $K_a = 3.3 \times 10^{-10}$
$H_2S$ has a greater $K_a$ value, therefore, it is more acidic.
So, $0.1M$ $H_2S$ is more acidic.
