A gaseous reaction system reaches equilibrium inside a cylinder fitted with a movable piston at a constant temperature and a constant external pressure of \(1.0 \text{ atm}\), as represented by the equation below. \[ \text{PCl}_5\text{(g)} \rightleftharpoons \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)} \] A sample of \(\text{Ar(g)}\) is injected into the cylinder at the same temperature while the external pressure remains constant at \(1.0 \text{ atm}\). Which of the following correctly predicts and explains the effect of adding \(\text{Ar(g)}\) on the number of moles of \(\text{Cl}_2\text{(g)}\) present when the system re-establishes equilibrium?