• The disturbance or the change in an Equilibrium occurs only when 1.) the partial pressures or 2.) the molar concentrations of the participants changes during the reaction.

• Adding inert gas while keeping the volume constant does not affect the Equilibrium because it cannot change either of the above-mentioned no.1.) or no.2.) major factors as it is not taking part in the reaction.

Hence for each cases of (i) H₂ (g) + I₂ (g) ⇋ 2HI (g)

(ii) PCI₅ (g) ⇋ PCI₃ (g) + CI₂ (g)

(iii) N₂ (g) +3H₂ (g) ⇋ 2NH₃ (g) the Equilibrium will remain unaffected on addition of Argon which is an inert gas.

Hence (iv) is the correct answer.