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JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Nucleus, Nuclear Reaction

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    Atomic weight of boron is 10.81 and it has two isotopes \[_{5}{{B}^{10}}\]and \[_{5}{{B}^{11}}\]. Then ratio of \[_{5}{{B}^{10}}{{:}_{5}}{{B}^{11}}\]in nature would be                  [CBSE PMT 1998; JIPMER 2001, 02]

    A)            19 : 81                                     

    B)            10 : 11

    C)            15 : 16                                     

    D)            81 : 19

    Correct Answer: A

    Solution :

                       Let the percentage of \[{{B}^{10}}\]atoms be x, then Average atomic weight                    \[=\frac{10x+11(100-x)}{100}=10.81\]\[\Rightarrow x=19\ \ \ \ \therefore \frac{{{N}_{{{B}^{10}}}}}{{{N}_{{{B}^{11}}}}}=\frac{19}{81}\]


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