JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    The number of alpha and beta particles emitted in the chain of reactions leading to the decay of\[_{92}^{238}U\]to\[_{82}^{206}Pb\]

    A)  \[8\] beta particles and \[6\] alpha particles

    B)  \[5\] alpha particles and \[0\] beta particles

    C)   \[8\] alpha and \[6\] beta particles

    D)   \[10\] alpha particles and \[10\] beta particles

    Correct Answer: C

    Solution :

    Key Idea: (i) Sum of atomic mass of reactants = sum of atomic mass of products. (ii) Sum of atomic number of reactants = sum of atomic number of products.                 \[_{92}{{U}^{238}}{{\xrightarrow{{}}}_{82}}P{{b}^{206}}+{{m}_{2}}H{{e}^{4}}+{{n}_{-1}}{{e}^{0}}\] where \[m=\]number of \[\alpha \] particles \[n=\]number of \[\beta \] particles \[\therefore \]  \[238=206+4\,\,m\] or               \[m=\frac{238-206}{4}\]             \[=\frac{32}{4}=8\] \[\therefore \]                  \[92=82+2m-n\] or            \[92-82=2\times 8-n\] or                    \[10=16-n\] \[\therefore \]            \[n=16-10=6\] \[\therefore \]  \[\alpha -\]particles emitted\[=8\]                    \[\beta \]particles emitted\[=6\]


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