A radioactive sample consists of two distinct species having equal number of atoms $N_0$ initially. The mean-life of one species is $\tau $ and of the other is $5\tau $. The decay products in both cases is stable. The total number of radioactive nuclei at $t = 5\tau $ is

  • A

    ${N_0}\left( {\frac{{{e^5} + 1}}{{{e^5}}}} \right)$

  • B

    ${N_0}\left( {\frac{{{e^4} + 1}}{{{e^5}}}} \right)$

  • C

    ${N_0}\left( {\frac{{e + {e^5}}}{{{e^5}}}} \right)$

  • D

    $N_0e^{-3}$

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