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. 0.75
C. 0.25
D. `6.25 %`

Answer

A

Explanation

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