Which of the following are true for order of a reaction?
A. It can be a fractional number.
B. It is applicable to complex reactions only.
C. It can have zero value.
D. It is an experimentally determined quantity.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
For a reaction whose experimentally found rate law is Rate = k[A]x[B]y, the order is the sum of the powers of the concentration terms:
\( \displaystyle \text{Order}=x+y \)
The powers x and y need not equal the coefficients in the balanced equation, so the order has to be found by experiment.
(A) It can be a fractional number. — Correct. For the decomposition of ethanal, Rate = k[CH3CHO]3/2, so the order is 1.5.
(B) It is applicable to complex reactions only. — Incorrect. Order applies to elementary as well as complex reactions. It is molecularity that applies only to elementary reactions.
(C) It can have zero value. — Correct. The decomposition of \( \ce{NH3} \) on a hot platinum surface at high pressure is zero order: Rate = k, independent of concentration.
(D) It is an experimentally determined quantity. — Correct. The order comes from the measured rate law, not from the balanced equation.
NCERT (2026-27 edition):
Molecularity of a Reaction – …
