When aqueous Ammonia is added to a solution of Zinc Nitrate until it goes into excess, and it is heated, a white precipitate comes into formation. This white precipitate is capable of dissolving in an excess solution of aqueous Ammonia so as to form a solution that is colorless. Upon further heating, a colorless, pungent gas gets evolved.
An excess of a solute in a solution means that the solution contains a greater amount by mass of the solute in comparison to the solvent. A pungent gas refers to a gas that has some odor, which is specific to its characteristics.