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J & K CET Medical J & K - CET Medical Solved Paper-2001

  • question_answer
    A radioactive isotope has a half-life of 10 days. What was its original weight 40 days earlier if today it is 125 g?

    A)  600 g                                    

    B)  1000 g

    C)  1250 g                                 

    D)  2000 g

    Correct Answer: D

    Solution :

                    \[{{t}_{1/2}}=10\text{ }days\] \[T=40\text{ }days\] \[n=\frac{T}{{{t}_{1/2}}}=\frac{40}{10}=4\]                 \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}={{\left( \frac{1}{2} \right)}^{4}}\]                 \[\frac{125}{{{N}_{0}}}=\frac{1}{16}\]                 \[{{N}_{0}}=2000\,g\]


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