The overall order of a reaction which has the rate expression
Rate \(= k [A]^{2/4}[B]^2\) will be
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(\frac{5}{2}\)
The order of a reaction is the sum of the powers of the concentration terms in the experimentally determined rate law. For Rate = k[A]x[B]y, the order is x + y. Here x = 2/4 and y = 2:
\( \displaystyle \text{Order} = \frac{2}{4} + 2 = \frac{1}{2} + 2 = \frac{5}{2} \)
So the order of the reaction is 5/2; an order can be a fraction.
NCERT (2026-27 edition):
Order of a Reaction – “In the rate equation (3.4) Rate = k [A]x [B]y, x and y indicate how sensitive the rate is to the change in concentration of A and B. Sum of these exponents, i.e., x + y in (3.4) gives the overall order of a reaction whereas x and y represent the order with respect to the reactants A and B respectively. Hence, the sum of powers of the concentration of the reactants in the rate law expression is called the order of that chemical reaction. Order of a reaction can be 0, 1, 2, 3 and even a fraction.”