At some instant, a radioactive sample $S_1$ having an activity $5\,\mu Ci$  has twice the number of nuclei as another sample $S_2$  which has an activity of  $10\,\mu Ci.$  The halflives of $S_1$  and  $S_2$ are

  • [JEE MAIN 2018]
  • A

    $10$ years  and  $20$ years, respectively

  • B

    $5$ years and $20$ years, respectively

  • C

    $20$ years  and  $10$ years,  respectively

  • D

    $20$ years  and $5$ years, respectively

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  • [AIIMS 2006]

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