Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2008

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

    A)  \[50\text{ }min\]         

    B)  \[100\text{ }min\]

    C) \[99\text{ }min\]     

    D)  \[150\text{ }min\]

    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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