Question

A radioisotope, tritium $\left({}_1^{3}H\right)$ has half life of $12.3$ years. If the initial amount of tritium is $32$ $mg$, how many milligrams of tritium would remain after $49.2$ years?

• A. $1$ $mg$
• B. $2$ $mg$
• C. $4$ $mg$
• D. $8$ $mg$

Answer 1

The correct option is B $2$ $mg$

Half life = 12.3 years

Therefore, 49.2 years = 4 half life

In each half life amount becomes half, after 4 half-lives amount becomes $\frac{1}{16}$. Therefore, amount remained =$\frac{32}{16}=2mg$.