In the given chemical reaction, ammonia gas (NH3) and hydrogen chloride gas (HCl) combine to form solid ammonium chloride (NH4Cl). The change in entropy of the system can be determined by comparing the entropy of the products with the entropy of the reactants. In this case, since the reactants are gases and the product is a solid, the overall entropy of the system decreases. Hence, the entropy change in the system is negative. Therefore, the correct option is "negative".