Question

# 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 is60153045

Solution

## The correct option is A 60We know that, N=N0e−λt For 40% decay, N1=N0−(40100)N0=(35)N0=0.6N0  For 85% decay, N2=N0−(85100)N0=(320)N0=0.15N0   N2N1=(12)2 So, two half life has passed. Since the half-life is 30 minutes, time taken for decay from 40% to 85% will be 2t1/2=2×30=60 minutes

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