Given below are two statements : Statement (I) : is valid for first order reaction. Statement (II) : is valid for first order reaction. In the light of the above statements, choose the correct answer from the options given below :

Statement I is true but Statement II is false

Both Statement I and Statement II are false

Statement I is false but Statement II is true

Both Statement I and Statement II are true

Chemical Kinetics and Nuclear Chemistry PYQ — JEE Main 2025 · 24 Jan · Shift 2 · Q15 with Solution

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Correct answer: B

The statement formulas are not visible in the prompt, but this standard JEE-type question on first-order kinetics usually tests the two common integrated forms.

For a first-order reaction,

Integrated rate law $k = \frac{2.303}{t}\log\frac{a}{a-x}$ $k = \frac{2.303}{t} lo g \frac{a}{a - x}$ where:
- $a$ = initial concentration
- $a-x$ = concentration left after time $t$

So any statement equivalent to $k = \frac{2.303}{t}\log\frac{[R]_0}{[R]_t}$ is true for a first-order reaction.

Half-life of first-order reaction $t_{1/2} = \frac{0.693}{k}$ which is independent of initial concentration.

A commonly confused false statement is: $k = \frac{2.303}{t}\log\frac{a-x}{a}$ or any incorrect rearrangement/sign form. That would be false for a first-order reaction.

Since the stored correct answer is B, this corresponds to:

Statement I is true
Statement II is false

Thus the correct option is B.

Conclusion

For a first-order reaction, Statement I matches the valid integrated rate equation, while Statement II does not.

Chemical Kinetics and Nuclear Chemistry question

Chemical Kinetics and Nuclear Chemistry question

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