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12th Class Chemistry Nuclear Chemistry / नाभिकीय रसायन Question Bank Critical Thinking Nuclear chemistry

  • question_answer
    Percentage of a radioactive element decayed after 20 sec when half-life is 4 sec                [BHU 2003]

    A)            92.25                                       

    B)            96.87

    C)            50  

    D)            75

    Correct Answer: B

    Solution :

           \[n=\frac{20}{4}=5,\frac{{{N}_{t}}}{{{N}_{o}}}={{\left( \frac{1}{2} \right)}^{5}}=\frac{1}{32},\,\,\therefore \text{decayed}\,\]                     \[=\left( \text{1--}\frac{\text{1}}{\text{32}} \right)\times 100=\frac{31}{32}\times 100=96.87\].


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