Question

If half life of a radioactive material is 5 years, then the percentage of it remained after 25 years will be

• A. 3.125%
• B. 6.25%
• C. 1.25%
• D. 25%

Answer 1

The correct option is A 3.125%

Half life of material $=5years=\frac{ln2}{k}$

where, $k$ is the decay constant.

Amount of material after time $t=N\left(t\right)=N_0{e}^{-kt}$

$\Rightarrow \frac{N}{N_0}=e^{-\frac{ln2}{5}25}$

$=e^{-5ln2}$

$=0.03125$

$=3.125$%