A) 23040 yr
B) 17280yr
C) 11520 yr
D) 5760 yr
Correct Answer: B
Solution :
\[{{t}_{1/2}}=5760\,yr\] \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] \[25=200{{\left( \frac{1}{2} \right)}^{n}}\] \[\frac{25}{200}={{\left( \frac{1}{2} \right)}^{n}}\] \[\frac{1}{8}={{\left( \frac{1}{2} \right)}^{n}}\] \[{{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{n}}\] \[n=3\] \[=3\times 5760\,yr\] \[=17280\,yr\]
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