$A$ radioactive substance has a half-life of $10^8$ years and an activity of $10^4 \,Bq$. The number of atoms of this substance present is

  • A
    $9.1 \times 10^{19}$
  • B
    $6.7 \times 10^9$
  • C
    $4.5 \times 10^{19}$
  • D
    $5 \times 10^{20}$

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The half-life of radium is $1620$ years and its atomic weight is $226 \, g/mol$. What is the number of atoms decaying per second in a $1 \, g$ sample? $[N_A = 6.023 \times 10^{23} \, \text{atoms/mol}]$

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If the half-life of a radioactive sample is $10\, hours$,its mean life is .......... $hours$.

The plot of the number $(N)$ of undecayed atoms versus activity $(A)$ of a radioactive substance is

In one average lifetime of a radioactive nucleus,

$A$ radioactive sample decays $\frac{7}{8}$ times its original quantity in $15$ minutes. The half-life of the sample is $......$ minutes.

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