NH4Cl(s) ↔ NH3(g) + HCL(g) The reaction above can only attain equilibrium if

In the given chemical reaction, NH4Cl(s) ↔ NH3(g) + HCl(g), the reaction can only attain equilibrium if it is in a closed system. This means that the reaction vessel must be closed so that the products and reactants cannot escape. In a closed system, the concentrations of the reactants and products reach a state of balance, which is known as equilibrium. Adding a gaseous reactant or removing one of the products will disturb the equilibrium and shift the reaction in the direction that minimizes the disturbance. Therefore, the only option that is necessary for the reaction to attain equilibrium is that it is in a closed system.