JIPMER Jipmer Medical Solved Paper-2009

  • question_answer
    If 50% of a radioactive substance dissociates in 15 min, then the time taken by substance to dissociate 99% will be

    A)  50 min                                 

    B)  100 min              

    C)         99 min                 

    D)         150 min

    Correct Answer: C

    Solution :

    Radioactive disintegration is a 1st order reaction, hence \[k=\frac{2.303}{t}\log \frac{a}{a-x}\] \[\therefore \]  \[k=\frac{2.303}{15}\log \frac{100}{100-50}\] also        \[k=\frac{2.303}{t}\log \frac{100}{100-99}\] \[\therefore \,\,\frac{2.303}{15}\log \frac{100}{50}=\frac{2.303}{t}\log \frac{100}{1}\] \[\frac{1}{15}\log 2=\frac{1}{t}\log 100\] \[\frac{0.3010}{15}=\frac{2}{t}\] \[t=\frac{2\times 15}{0.3010}=99\,\min \]


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