JEE Main & Advanced Sample Paper JEE Main - Mock Test - 6

  • question_answer
    An element with mass number 81 contains \[31.7%\] more neutrons as compared to protons. Find the symbol of the atom.

    A) \[_{34}^{81}Se\]         

    B) \[_{35}^{81}Br\]  

    C) \[_{36}^{81}Kr\]         

    D) \[_{37}^{81}Rb\]

    Correct Answer: B

    Solution :

    Mass number of element = 81 i.e. \[p+n=81\]
    Let the number of protons be x.
    Number of neutrons \[=x+\frac{31.7}{100}\times x=1.317x\]
    \[\therefore \,\,\,x+1.317x=81\]  or  \[2.317x=81\]
    or         \[x=\frac{81}{2.317}=35\]
    Symbol of the element \[=\,_{35}^{81}Br\]

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