Question

The half-life period of a radioactive element is 140 days. After 650 days, one gram of the element will reduce to

• A. $\frac{1}{2}g$
• B. $\frac{1}{4}g$
• C. $\frac{1}{8}g$
• D. $\frac{1}{16}g$

Answer 1

Answer: (D)

$\frac{1}{16}g$

Answer 2

560 daya $=\frac{560}{140}$ =4 half-lives
Amount of reactant remaining after /z-half-lives
$=\bigg(\frac{1}{2}\bigg)^n\times$ initial amount $=\bigg(\frac{1}{2}\bigg)^4\times1.0g=\frac{1}{16}g$