Answer
$(c) 0.40M$ $CH_3COOH$
Work Step by Step
1. Compare the Ka values for each acid.
$HCOOH: 1.77 \times 10^{-4}$
$HClO_4 > 1 (Strong$ $acid)$
$CH_3COOH: 1.76 \times 10^{-5}$
2. The one with the lowest Ka value is the $CH_3COOH$.
- With a lower Ka, the $[H^+]$ in a solution with the acid will be lower. (If the acids are in the same concentration)
- With a lower concentration of $H^+$, the pH will be higher.
