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Chemistry Question 57 – JEE-MAIN 2026

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Consider the reaction aX→bY, for which the rate constant at 30∘C is 1×10−3 mol−1 L s−1. Which of the following statements are true ? A. When concentration of 'X' is increased to four times, the rate of reaction becomes 16 times. B. The reaction is a second order reaction. C. The half-life period is independent of the concentration of X. D. Decomposition of N2O5 is an example of the above reaction. E. The graph of In[R0][R] vs time (showing a straight line with positive slope) is valid for the above reaction.

The units of the rate constant directly indicate the overall order of a chemical reaction.

Step 1: Determine the Order of the Reaction✦ Active

The given rate constant is k=1×10−3 mol−1 L s−1. The general units for a rate constant of order n are mol1−n Ln−1 s−1. Comparing the exponents:

1−n=−1⟹n=2 n−1=1⟹n=2

Thus, the reaction is a **second-order reaction**.

Step 2: Evaluate Each Statement○ Expand

Based on the reaction being second-order:

A. For a second-order reaction, Rate =k[X]2. If [X] is increased to 4[X], Rate' =k(4[X])2=16k[X]2=16×Rate. So, statement A is **TRUE**.

B. As determined, the reaction is second-order. So, statement B is **TRUE**.

C. For a second-order reaction, the half-life t1/2=1k[X]0. It depends on the initial concentration [X]0. So, statement C is **FALSE**.

D. Decomposition of N2O5 is a well-known first-order reaction. The given reaction is second-order. So, statement D is **FALSE**.

E. The graph of In[R0][R] vs time is characteristic of a first-order reaction. The given reaction is second-order. So, statement E is **FALSE**.

💡 Teacher's Secret Hint

Remember the specific characteristics (rate law, half-life, integrated rate law plots) for different orders of reactions.

Step 3: Identify the Correct Option○ Expand

Only statements A and B are true. Therefore, the correct option is "A and B Only".

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