JEE Main 2026 — Chemical Kinetics Question with Solution

The unit of the rate constant $k$ is mol${}^{-1}$ L s${}^{-1}$.

The general unit of the rate constant for an $n$-th order reaction is (mol L${}^{-1}$)${}^{1-n}$ s${}^{-1}$.

Equating the powers of the concentration units, we get $1-n=-1\Rightarrow n=2$.

Thus, the reaction is a second-order reaction. Statement B is correct.

For a second-order reaction, Rate $=k[X{]}^2$. When the concentration of $X$ is increased to $4$ times, the new rate is $k(4[X]{)}^2=16k[X{]}^2$, which is $16$ times the original rate. Statement A is correct.

The half-life of a second-order reaction is $t_{1/2}=\frac{1}{k[X{]}_0}$, which depends inversely on the initial concentration. Statement C is incorrect.

The decomposition of $N_2{O}_5$ is a well-known first-order reaction. Statement D is incorrect.

The equation $\ln \frac{[R_o]}{[R]}=kt$ represents the integrated rate law for a first-order reaction, not a second-order reaction. Statement E is incorrect.

Therefore, only statements A and B are correct.

Answer: A and B Only