NH3(g) + HCl(g) -> NH4Cl(s). What kind of reaction is this?
NH3(g) + HCl(g) -> NH4Cl(s). What kind of reaction is this?
Since two reactants (ammonia gas and hydrogen chloride gas) combine to form a single product (ammonium chloride), this is a combination (addition) reaction.
Re-check your working by substituting the answer back into the original question.