What is the over all order of reaction which has the following rate expression ?
Rate = k[A]1/2 [B]3/2
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Two
The order of a reaction as a whole is the sum of the powers of the concentration terms in the rate law. Orders are found by experiment and may be fractions.
\( \displaystyle \text{Rate}=k[\mathrm{A}]^{1/2}[\mathrm{B}]^{3/2} \)
\( \displaystyle \text{Order}=\frac{1}{2}+\frac{3}{2}=2 \)
So the order of the reaction is two: half order in A and three-half order in B.
Note 1: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27 edition):
Order of a Reaction – Example 3.3: “Calculate the overall order of a reaction which has the rate expression (a) Rate = k [A]1/2 [B]3/2 … (a) Rate = k [A]x [B]y order = x + y So order = 1/2 + 3/2 = 2, i.e., second order”
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | 19-07 S1 29-05 S1 | – | – |