JEE Main levelSingle correct optionDifficulty 2 of 3ck038
A first order reaction has a half-life of 10min. The percentage of the reactant left after 25min is closest to
A18.75%
B12.5%
C25.0%
D17.7%
Answer: D
25min=2.5 half-lives, so the fraction left is (1/2)2.5=0.1768, i.e. 17.7%. Linear interpolation between 25% and 12.5% (giving 18.75%) is wrong because decay is exponential.