Q80 / 200 · NEET 2003 · Chemistry

The radiosotope tritium $\left({ }_1^3 \mathrm{H}\right)$ has a lalf life of 12.3 years. If the initial amount of tritium is $32 \mathrm{mg}$, how many milligrams of it would remain after 49.2 years

  • A
    $1 \mathrm{mg}$
  • Correct answer
    B
    $2 \mathrm{mg}$
  • C
    $4 \mathrm{mg}$
  • D
    $8 \mathrm{mg}$

Solution

$$ \begin{aligned} \mathrm{T} & =\mathrm{t}^{1 / 2} \times n \\ n & =\frac{49.2}{12.3}=4 \\ \mathrm{~N} & =\mathrm{N}_0(1 / 2)^n \\ & =32(1 / 2)^4 \\ & =2 \mathrm{mg} \end{aligned} $$

Hence, the correct answer is option: 'B'.

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