The decay constant of a radio isotope is $\lambda$. If  $A_1$ and $A_2$ are its activities at times $t_1$ and $t_2$  respectively, the number of nuclei which have decayed during the time $(t_1 - t_2)$ 

  • [AIPMT 2010]
  • A

    $A_1t_1-A_2t_2$

  • B

    $A_1-A_2$

  • C

    $(A_1-A_2)/λ$

  • D

    $λ (A_1-A_2)$

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  • [JEE MAIN 2020]