A) 0.5
B) 0.25
C) 0.125
D) 0.33
Correct Answer: C
Solution :
If N be the number of atoms of a radioactive substance left at some instant of time, then \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] where \[{{N}_{0}}\] is the initial number of atoms and n is number of half-lives. \[\therefore \,\,\,\,\,\,\,\,\,n=\frac{t}{T/2}=\frac{30}{10}=3\] \[\therefore \,\,\,\,\,\,\,\,\,\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{3}}\] \[=\,\,\,\,\,{{\left( \frac{1}{2} \right)}^{3}}=\frac{1}{8}=0.125\]
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