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JEE Main & Advanced Sample Paper JEE Main Sample Paper-27

  • question_answer
    An element X has atomic mass of 200 amu. If it has two isotopes as \[{{\mathbf{X}}^{\mathbf{201}}}\] & \[{{\mathbf{X}}^{\mathbf{198}}},\] the percentage of \[{{\mathbf{X}}^{\mathbf{201}}}\] is:

    A)  \[33.33%\]                   

    B)  \[66.67%\]

    C)  \[50%\]                        

    D)  \[25%\]

    Correct Answer: B

    Solution :

    \[\frac{{{a}_{1}}{{m}_{1}}\,+{{a}_{2}}{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}}\,=200\] \[{{a}_{1}}:\] mass of I isotope \[{{m}_{1}}:\] :% of I isotope \[{{a}_{2}}:\] mass of II isotope \[{{m}_{2}}:\] % of ll isotope \[\frac{201x+198(100-x)}{x+(100-x)}\,=200\] \[\frac{201x+19800-198x}{100}=200\] \[x=66.67%\]


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