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For a radioactive material, half-life is 10 minutes. If initially there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is:

1. 20
2. 10
3. 15
4. 30

Correct answer: 20

Solution

The half-life is 10 minutes, so after 10 minutes, half of the nuclei (300) will remain. After another 10 minutes (20 minutes total), half of the remaining 300 nuclei (150) will remain, leaving 450 nuclei disintegrated. Thus, the time taken is 20 minutes.

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