A) 0.125 mg
B) 0.5 mg
C) 0.25 mg
D) 0.91 mg
Correct Answer: A
Solution :
From Rutherford and Soddy law, at any instant, the rate of decay of a radioactive substance is proportional to the amount of the substance left at that instant. The amount left after n half-lives is \[M={{M}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] where,\[{{M}_{0}}\]is original amount of substance atoms. Given, \[n=\frac{8.1}{2.7}=3,{{M}_{0}}=1\,mg\] \[\therefore \] \[M=1{{\left( \frac{1}{2} \right)}^{3}}=\frac{1}{8}mg=0.125\,mg\]
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