What will happen to the chemical equilibrium if NH4Cl is added to this solution?

The answer to this item depends entirely to the chemical reaction. If the compound, NH4Cl, is in the left hand side of the reaction, when it is added, the reaction will shift to the left. In the same manner, when the compound is in the right-hand side of the reaction, the reaction will shift to the right.

This happens because initially the reaction is in equilibrium and adding another compound to it will most likely lead to the shifting of the reaction.