Question

# The half life of a radioactive substance is 30 minutes. The time taken between 40% decay and 85% decay of the same radioactive substance in minutes is:15603045

Solution

## The correct option is B 60t1/2=30 min N1=N0(12)T130N2=N0(12)T230 N1=100−40=60 N1 = Atom remains undecay N2 = 100-85 N2 = Atom remains undecay 60=N0(12)T130               ⋯(1) 15=N0(12)T130              ⋯(2) By (1) and (2) 4=(12)T1−T230 4=2−(T1−t2)30 (2)2=(2)30T1−T2 2=T1−T230 T2−T1=60 min

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