The half-life period of a radioactive substance is `5 min`. The amount of substance decayed in `20 min` will be

Options

A. `93.75%`
B. `75%`
C. `25%`
D. `6.25%`

Answer

A

Explanation

Number of half lives in 20 min `=n=(20)/(5)=4`
Fraction of material rermains after four half lives `=(1)/(16)`
Hence fraction that decays `=1-(1)/(16)=(15)/(16) = 93.75%`