The half-life of a first order reaction is 25 minutes. Its rate constant is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(2.8 × 10^{-2} min^{-1}\)
For a first order reaction the half-life does not depend on the initial concentration:
\( t_{1/2} = \displaystyle\frac{0.693}{k} \Rightarrow k = \displaystyle\frac{0.693}{t_{1/2}} \)
With t1/2 = 25 min:
\( k = \displaystyle\frac{0.693}{25\ \text{min}} = 0.0277\ \text{min}^{-1} \approx 2.8 \times 10^{-2}\ \text{min}^{-1} \)
The rate constant is 2.8 × 10−2 min−1.
NCERT (2026-27 edition):
Half-Life of a Reaction
