Dissolving $NaCN$ in de-ionised water will result in a solution having

$0.5 \, M$ ammonium benzoate is hydrolysed to $0.25 \%$ percent,hence its hydrolysis constant is

Explain the following with reasons:
$(i)$ $NaCl$ solution is neutral. The solution of strong acid and strong base salts is neutral.
$(ii)$ $NaCH_3COO$ solution is basic. The solution of strong base and weak acid salt is basic.
$(iii)$ $NH_4Cl$ solution is acidic. The solution of weak base and strong acid salt is acidic.
$(iv)$ The solution of $NH_4CH_3COO$ is (almost) neutral. The solution of weak acid - weak base salts is almost neutral.

Arrange the aqueous solutions of the following salts in the increasing order of $pH$: $CuSO_4$ $(I)$,$NaCN$ $(II)$,$KCl$ $(III)$.

$A$ weak acid with $pK_a$ $5.9$ and a weak base with $pK_b$ $5.8$ are mixed in equal proportions. The $pH$ of the resulting solution is:

An aqueous solution of aluminum chloride is acidic due to $........$.