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CMC Medical CMC-Medical VELLORE Solved Paper-2011

  • question_answer
    A radioactive isotope has a half-life of 8 days. If today 125 mg is left over, what was its original weight 32 days earlier?

    A)  6 g                                        

    B)  5 g

    C)  4 g                                        

    D)  2 g

    E)  1 g

    Correct Answer: D

    Solution :

                                    \[T=n\times {{t}_{1/2}}\] \[\Rightarrow \]               \[32=n\times 8\] \[\therefore \]  \[n=4\] \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] \[\Rightarrow \]               \[125={{N}_{0}}{{\left( \frac{1}{2} \right)}^{4}}\] \[125={{N}_{0}}\times \frac{1}{16}\] \[N=125\times 16=2000\,mg=2g\]


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