Question

A solution of $N{H}_{4}Cl$ and $N{H}_{4}OH$ acts as a buffer.

Answer 1

$N{H}_{4}Cl$ is a strong electrolyte hence, dissociates completely, $N{H}_{4}OH$ is a weak electrolyte. Its dissociation is further suppressed by common ion $N{H}_4^{+}$ provided by $N{H}_{4}Cl$ in the solution.
$N{H}_{4}C{l}_{aq}\rightleftharpoons N{H}_{4_{aq}}^{+}+C{l}_{aq}^{-}$
$N{H}_{4}O{H}_{aq}\rightleftharpoons N{H}_{4_{aq}}^{+}+O{H}_{aq}^{-}$
This solution acts as a basic buffer and maintains its $pH$ around $9.25$. It is capable of resisting the change in $pH$ on addition of small amount of acid or alkali.
To Explain:
If a small amount of $HCl$ is added to this solution, $H^{+}$ ions of $HCl$ get neutralized by $O{H}^{-}$ ions already present and more of $N{H}_{4}OH$ molecules get ionized to compensate loss of $O{H}^{-}$ ions. Thus $pH$ practically, remains constant.
If a small amount of $NaOH$ is added to this solution, $O{H}^{-}$ ions of $NaOH$ combine with $N{H}_4^{+}ions$ already present in large number forming weakly ionized $N{H}_{4}OH$. Thus, $pH$ of solution remains practically unchanged.