CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2001

  • question_answer
    A radioactive isotope has a half life of 10 years. What percentage of the original amount of it remain after 20 years:

    A)  0                                            

    B)  12.5

    C)  8                                            

    D)  25

    Correct Answer: D

    Solution :

    We know that\[{{C}_{n}}=\frac{{{C}^{o}}}{{{2}^{n}}}\] \[{{C}_{n}}=\]concentration after n half-lives \[n=\]number of half-lives \[{{C}^{o}}=\]initial concentration \[{{C}_{n}}=\frac{1}{{{2}^{2}}}=\frac{1}{4}=0.25\]or \[25%\]


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