Read the passage carefully and answer the questions based on the passage:
The number of reacting species (atoms, ions or molecules) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction is called molecularity of a reaction. In the rate equation Rate = \( k [A]^x [B]^y \)
\( x \) and \( y \) indicate how sensitive the rate is to the change in concentration of A and B, respectively. Sum of these exponents, i.e., \( x + y \) gives the overall order of a reaction where \( x \) 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. For a first order reaction, the concentration of the reactant varies as \( [R] = [R]_0e^{-kt} \)
The conversion of molecules X to Y follows second order kinetics. If the concentration of X is increased to four times, how does it affect the rate of formation of Y?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The rate will increase by 16 times
For a reaction of order n in X, the rate depends on [X]n. A second order reaction has the rate law:
\( \text{Rate} = k[X]^2 \)
When [X] is made four times:
\( \text{Rate}' = k(4[X])^2 = 16\,k[X]^2 = 16 \times \text{Rate} \)
So the rate of formation of Y increases 16 times.
Note 1: NTA picked this question from an NCERT (2026-27) intext question and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27 edition):
Molecularity of a Reaction – “… The conversion of molecules X to Y follows second order kinetics. If concentration of X is increased to three times how will it affect the rate of formation of Y?”
Rate Expression and Rate Constant – “… 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.”
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 |
|---|---|---|---|---|
| – | 15-05 S2 | – | 10-06 S3 | – |