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Question:

The half-life of a radioactive nucleus is 50 days. The time interval (t2−t1) between the time t2 when 2/3 of it has decayed and the time t1 when 1/3 of it had decayed is:

50days

15days

30days

60days

Solution:

Radioactive substance disintegrates 2/3rd in time t2 and 1/3rd in time t1. When it disintegrates 2/3rd to 1/3rd. It becomes 1/2. So time t2−t1 is half-life of substance. That is, 50 days