Answer:
synthesis
Step-by-step explanation:
The reaction given is a synthesis reaction or combination reaction.
Given equation:
NH₃ + HCl → NH₄Cl
In a synthesis reaction, a single product is formed from two or more reactants
A + B → C
The formation of compounds from the union of constituent elements also falls into this category.
So the given reaction is a synthesis reaction.
In a decomposition reaction two or more products are formed from a single reactant
In a single replacement reaction, one substance replaces another.
In double replacement reactions partners in a chemical specie are exchanged.
Therefore the given reaction is a synthesis reaction