JEE Main 2025 Apr 3 Shift 1, Chemistry Q15: Factors Affecting Equilibria

At constant temperature and total pressure, adding an inert gas (Xe) forces the system to expand to keep $P$ fixed. The volume increase lowers the partial pressures of every reactive species.

For ${\text{PCl}}_5\rightleftharpoons {\text{PCl}}_3+{\text{Cl}}_2$, the number of gaseous moles increases on the product side ($1\to 2$). By Le Chatelier, the equilibrium shifts toward the side with more moles to oppose the drop in pressure, i.e. the forward direction.

$\therefore$ $[{\text{PCl}}_5]$ decreases while $[{\text{PCl}}_3]$ and $[{\text{Cl}}_2]$ both increase. Among the given options, only the statement that $[{\text{PCl}}_3]$ increases is correct.