Match List-I with List-II.
| List-I (Reaction) | List-II (Order of the reaction) |
|---|---|
| (A) \( \ce{2NH3(g) -> N2(g) + 3H2(g)} \) on a hot platinum surface at high pressure | (I) Second order |
| (B) \( \ce{2N2O5(g) -> 4NO2(g) + O2(g)} \) | (II) Zero order |
| (C) \( \ce{KClO3 + 6FeSO4 + 3H2SO4 -> KCl + 3Fe2(SO4)3 + 3H2O} \) | (III) Third order |
| (D) \( \ce{2NO(g) + O2(g) -> 2NO2(g)} \) | (IV) First order |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-II, B-IV, C-I, D-III
The order of a reaction is the sum of the powers of the concentrations in its rate law, found by experiment. It need not match the coefficients of the balanced equation.
(A) \( \ce{2NH3(g) -> N2(g) + 3H2(g)} \) on a hot platinum surface at high pressure — This matches (II) Zero order. The platinum surface is saturated with ammonia, so Rate = k[NH3]0 = k.
(B) \( \ce{2N2O5(g) -> 4NO2(g) + O2(g)} \) — This matches (IV) First order. The rate depends on the first power of [N2O5], not on its coefficient 2.
(C) \( \ce{KClO3 + 6FeSO4 + 3H2SO4 -> KCl + 3Fe2(SO4)3 + 3H2O} \) — This matches (I) Second order. It looks tenth order (1 + 6 + 3), but it takes place in several steps and is found to be second order.
(D) \( \ce{2NO(g) + O2(g) -> 2NO2(g)} \) — This matches (III) Third order. Rate = k[NO]2[O2], so the order is 2 + 1 = 3.
NCERT (2026-27 edition):
3.3.1 Zero Order Reactions – “The decomposition of gaseous ammonia on a hot platinum surface is a zero order reaction at high pressure.”
3.3.2 First Order Reactions – “Decomposition of N2O5 and N2O are some more examples of first order reactions.”
3.2.4 Molecularity of a Reaction – “This reaction which apparently seems to be of tenth order is actually a second order reaction.”
3.2.2 Rate Expression and Rate Constant – “Hence, the rate equation for this reaction will be Rate = k [NO]2[O2]”