Le Chatlier's principle is applicable when
(i) `Fe(s)` and `S(s)` react to form `FeS(s)`
(ii) `PCl_5(g)` decomposes to form `PCl_3(g)` and `Cl_2(g)`
(iii) `N_2(g)` and `H_2(g)` react to form `NH_3(g)`
(iv) `H_2(g)` and `I_2(g)` react to form `HI(g)`

Options

A. (i), (ii), (iii), (iv)
B. (i), (ii), (iii)
C. (ii), (iii), (iv)
D. (i), (iii), (iv)

Answer

C

Explanation

Le Chatlier's principle states that if an external stress is applied to a system at equilibrium, the system adjusts itself in such a way that the stress is partially offset. The word "stress" here means a change in concentration, pressure, volume, or temperature that removes a system from the equilibrium state.
Reaction (i) is irreversible and, thus, cannot attain the state of equilibrium. Le Chatelier's principle is of no use in this reaction.