A radioactive nucleus $A$ with a half life $T$, decays into a nucleus $B.$ At $t = 0$, there is no nucleus $B$. At sometime $t$, the ratio of the number of $B$ to that of $A$ is $0.3$. Then, $t$ is given by

  • [JEE MAIN 2017]
  • A

    $t  = \frac{T}{2}\;\frac{{\log 2}}{{\log 1.3}}$

  • B

    $t = T\;\frac{{\log 1.3}}{{\log 2}}$

  • C

    $t=T \log(1.3)$

  • D

    $t = \frac{T}{{{{log}}\left( {1.3} \right)}}$

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  • [JEE MAIN 2020]

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$(II)$ Half life time of a radioactive element is time required for one half of the radioactive atoms to disintegrate

$(III)$ Age of earth can be determined with the help of radioactive dating

$(IV)$ Half life time of a radioactive element is $50\%$ of its average life periodSelect correct answer using the codes given belowCodes :