Haryana PMT Haryana PMT Solved Paper-2003

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

    A)  50 minutes     

    B)  100 minutes

    C)  99 minutes     

    D)  150 minutes

    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,       \[k=\frac{2.303}{t}\log \frac{100}{100-99}\]                 \[\therefore \]  \[\frac{2.303}{15}\log \frac{100}{50}=\frac{2.303}{t}\log \frac{100}{l}\]                                 \[\frac{1}{15}\log 2=\frac{1}{t}\log 100\]                                 \[\frac{0.3010}{15}=\frac{2}{t}\]                 \[\therefore \]  \[t=\frac{2\times 15}{0.3010}\]                                 \[=99\] minutes


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