The half-life of a radioactive substance is `30` minutes, The time (in minutes) taken between `40 %` decay and `85 %` decay of the same radioactive substance is.

Options

A. 45
B. 60
C. 15
D. 30

Answer

B

Explanation

Decay `40% rarr 85%`
Remaining `60% rarr 15%`
`60% overset(t_(1//2))rarr 30% overset(t_(1//2))rarr 15%`
`therefore t= 2t_(1//2) = 60` min