Which of the following pairs show common ion effect?


> 
> Which of the following pairs show common ion effect?
> 
> 
> 1. $\ce{BaCl2}$,$\ce{Ba(NO3)2}$
> 2. $\ce{NaCl}$, $\ce{HCl}$
> 3. $\ce{NH4OH}$,$\ce{NH4Cl}$
> 4. $\ce{NaOH}$, $\ce{NaCl}$
> 
> 
> 


Its not (1) because they are both solids.


The remaining are solute solvent pairs. So all the other pairs will show common ion effect if the solute is soluble to some extent and exists in an equilibrium with the solvent. The answer given is (3). But why cant (2) and (4) show common ion effect?


