Question

A radioactive isotope has a half life of one day. After three days, the fraction of original amount of element left will be :

• A. 1/2
• B. 1/8
• C. 1/4
• D. 1/6

Answer 1

The correct option is B 1/8

$t_{\frac{1}{2}}=oneday$
$\therefore$ 2t means amount will be reduced to half of the initial, after a day.
Day-1] $a_0$ will become $\frac{a_0}{2}$

Day-2] $\frac{a_0}{2}$ will become $\frac{a_0}{4}$

Day-3] $\frac{a_0}{2}$ will become $\frac{a_0}{8}$
where $a_0$ is the initial amount.