CUET · CHEMISTRY · PYQ PAPER 2025

Half life of the zero order reaction is:

A Directly proportional to the square root of the initial concentration of the reactant
B Independent of initial concentration of the reactant
C Inversely proportional to initial concentration of the reactant
D Directly proportional to initial concentration of the reactant

Verified Solution

Answer & Solution

Correct Answer

(D) Directly proportional to initial concentration of the reactant

Step-by-step Solution

Detailed explanation

For zero order reaction: \( [A] = [A]_0 - kt \) At \( t_{1/2} \), \( [A] = \frac{[A]_0}{2} \) \( \frac{[A]_0}{2} = [A]_0 - kt_{1/2} \) \( t_{1/2} = \frac{[A]_0}{2k} \) Directly proportional to initial concentration of the reactant.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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