The activity of a radioactive material is $6.4 \times 10^{-4}$ curie. Its half life is $5\; days$. The activity will become $5 \times 10^{-6}$ curie after $.......day$

  • [JEE MAIN 2022]
  • A

    $7$

  • B

    $15$

  • C

    $25$

  • D

    $35$

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