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

Step-by-step solution

When 40 % nuclei decay, 60 % nuclei remain undecayed Let this number be N ₀ When 85 % nuclei decay, 15 % nuclei remain undecayed This number will be N = N ₀ 4 The number of nuclei will become one-fourth in two half-lives i.e., 60 minutes.