Question

Which of the following pair will not show
common ion effect :

Answer 1

Explanation:

Common ion effect is observed when a solution of weak electrolyte is mixed with a solution of strong electrolyte which provides an ion common to that provided by a weak electrolyte.

Ammonium hydroxide is a weak electrolyte and ammonium chloride is a strong electrolyte. Ammonium chloride provides ammonium ions common to ammonium hydroxide.

Thus, the pair NH4OH+NH4Cl shows common ion effect. 

All other pairs have a mixture of strong electrolytes mixed with strong electrolyte hence they do not show common ion effect.