Answer:-  

The common ion effect defines the change in equilibrium that results from the addition of a common ion, which is an ion that is already present in the solution. A solution becomes less soluble generally due to the common ion effect.
Hydrogen cyanide (HCN) won’t ionise as a result of the addition of HCl, which will also cause an equilibrium shift to the left. The hydrogen ions will be reduced as a result of a drop in the hydrogen cyanide dissociation percentage, which will raise the pH of the solution.