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.

(N/A) $(i)$ Sodium chloride $(NaCl)$ is a salt of strong acid $(HCl)$ and strong base $(NaOH)$. In $NaCl$ solution,$Na^{+}$ and $Cl^{-}$ are hydrated ions.
$NaCl \longrightarrow Na^{+}{(aq)} + Cl^{-}{(aq)}$
$Na^{+}$ and $Cl^{-}$ ions do not undergo hydrolysis. So,the $pH$ of $NaCl$ solution is equal to the $pH$ of water $(7)$. Thus,this solution is neutral.
$(ii)$ Sodium acetate is a salt of strong base $(NaOH)$ and weak acid $(CH_3COOH)$.
$CH_3COONa{(aq)} \longrightarrow Na^{+}{(aq)} + CH_3COO^{-}{(aq)}$
$Na^{+}$ is not hydrolyzed. The acetate ion $(CH_3COO^{-})$ undergoes hydrolysis with water to produce weak acid $CH_3COOH$ and $OH^{-}$ ions.
$CH_3COO^{-}{(aq)} + H_2O_{(l)} \rightleftharpoons CH_3COOH{(aq)} + OH^{-}{(aq)}$
Since $CH_3COOH$ is a weak acid,it remains largely undissociated. This increases the $[OH^{-}]$ concentration,making the solution basic $(pH > 7)$.
$(iii)$ Ammonium chloride $(NH_4Cl)$ is a salt of weak base $(NH_4OH)$ and strong acid $(HCl)$.
$NH_4Cl{(aq)} \longrightarrow NH_4^+{(aq)} + Cl^{-}{(aq)}$
Ammonium ions $(NH_4^+)$ undergo hydrolysis to form $NH_4OH$ and $H^{+}$ ions.
$NH_4^+{(aq)} + H_2O_{(l)} \rightleftharpoons NH_4OH{(aq)} + H^{+}{(aq)}$
Since $NH_4OH$ is a weak base,it remains largely undissociated. This increases the $[H^{+}]$ concentration,making the solution acidic $(pH < 7)$.
$(iv)$ Ammonium acetate $(NH_4CH_3COO)$ is a salt of weak base $(NH_4OH)$ and weak acid $(CH_3COOH)$. Both ions undergo hydrolysis.
$CH_3COO^{-}{(aq)} + NH_4^+{(aq)} + H_2O_{(l)} \rightleftharpoons CH_3COOH{(aq)} + NH_4OH{(aq)}$
The $pH$ of the solution depends on the relative dissociation constants of the acid and base: $pH = 7 + \frac{1}{2}(pK_a - pK_b)$. If $pK_a = pK_b$,the solution is neutral.