NEET Sample Paper NEET Sample Test Paper-9

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

    A)  \[600\text{ }g\]                      

    B) \[1000\text{ }g\]

    C)  \[1250\text{ }g\]                    

    D) \[2000g\]

    Correct Answer: D

    Solution :

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

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