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In a first-order reaction A → B, if k is rate constant and initial concentration of the reactant A is 0.5 M, then the half-life is

1. log 2 / k
2. log 2 / k√0.5
3. ln 2 / k
4. 0.693 / k

Correct answer: 0.693 / k

Solution

For a first-order reaction, the half-life (t₁/₂) is given by the formula t₁/₂ = 0.693 / k, which is independent of the initial concentration of the reactant.

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