Answer:
Because ammonium chloride is not soluble in dichloromethane solvent.
Step-by-step explanation:
It looks like you are trying to do a Williamson ether synthesis using 2-naphthol, allyl chloride, and a phase transfer catalyst like benzyltriphenylammonium chloride.
The phase transfer catalyst is soluble in dichloromethane and carries the alkoxide ions with it into the organic phase. This is where the reaction takes place.
If, instead, you use ammonium chloride, the reaction will fail.
NH₄Cl is a polar ionic solute. It is soluble in the polar aqueous phase but insoluble in the much less polar dichloromethane.
A is wrong. Naphthols do not undergo displacement reactions.
B is wrong. NH₄Cl generates the weak base NH₃ in aqueous NaOH.
D is wrong. Ammonium salts are soluble in water.