Which of the following is an acidic salt?

The $pH$ of an aqueous solution of alum is ....

Calculate $[H^{+}]$ at the equivalence point during the titration of $25 \ mL$ of $0.1 \ M$ weak acid $HA$ $(K_a = 10^{-5})$ with $0.05 \ M \ NaOH$ solution.

The aqueous solution of $CH_3COONa$ is .......

The aqueous solution of which of the following salts has the lowest $pH$?

An aqueous solution of potassium formate is ...........