The half-life of a radioactive substance is 30 min . The time (in minutes) taken between 40 % decay and 85 %…

The half-life of a radioactive substance is 30 min. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is
  1. 15
  2. 30
  3. 45
  4. 60

Solution

Number of active nuclei falls from 60% to 15%
So the sample becomes 14th
=122th
So the number of half-lives = 2
Time t=2×30=60 min

Asked in: NEET 2016 (Phase 2)

Practice more Structure of Atoms and Nuclei questions on Aicharya