A) 40 yr
B) 60 yr
C) 80 yr
D) 100 yr
Correct Answer: B
Solution :
| As \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] |
| \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{3}}=\frac{1}{8}\] |
| Number of half-lives = 3 |
| \[\Rightarrow \] \[T=20\,\,yr\] |
| \[\therefore \] \[T=\frac{t}{n}\] |
| or \[t=T\times n=20\times 3yr=60\,yr\] |
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