Two radioactive materials $A$ and $B$ have decay constants $25 \lambda$ and $16 \lambda$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of $B$ to that of $A$ will be "$e$" after a time $\frac{1}{a \lambda}$. The value of $a$ is $......$

  • [JEE MAIN 2022]
  • A

    $9$

  • B

    $8$

  • C

    $5$

  • D

    $6$

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