Question

The half-life of a radio active substance is 20 min. The approximate time interval $(t_2–t_1)$ between the time $t_2$ when $\frac{2}{3}$ of it has decayed and time $t_1$ when $\frac{1}{3}$ of it had decayed is:

• A. 7 min
• B. 14 min
• C. 20 min
• D. 28 min

Answer 1

The correct option is C 20 min

$\frac{2}{3}{A}_0\stackrel{t_{\frac{1}{2}}}{\to }\frac{1}{3}{A}_0$
$t_{\frac{1}{2}}=20min$