Question

Addition of ${NH}_{4}Cl$ does not effect the $pH$ of solution of ${NH}_{4}OH$.

If true write 1, else write 0.

Answer 1

Adding a common ion prevents the weak acid or weak base from ionizing as much as it would without the added common ion. The common ion effect suppresses the ionization of a weak acid by adding more of an ion that is a product of this equilibrium.

So the addition of ${NH}_{4}Cl$ reduces dissociation of ${NH}_{4}OH$ and because of that its pH will decrease.