Answer
$0.10M$ $K_2S$ is more basic.
Work Step by Step
** You can find the $K_b$ values on table: 14.2 (Page 624)
Since both solutions have the same concentration, we just have to determine which compound is more basic:
-$K_2S$:
It is a salt formed by $2K^+$ and $S^{2-}$.
$K^+$ has negligible acidity, so, we don't need to consider it.
$S^{2-}$ is a strong base with $K_b = 1 \times 10^{5}$
- $K_3PO_4$:
It is a salt formed by $3K^+$ and $P{O_4}^{3-}$.
$K^+$ has negligible acidity, so, we don't need to consider it.
$P{O_4}^{3-}$ is a base with $K_b = 2.2 \times 10^{-2}$
$S^{2-}$ has a greater $K_b$ value, therefore, it is more basic.
So, $0.10M$ $K_2S$ is more basic.
