Half-life of a radioactive substance is 20 minutes. The time between 20% and 80% decay will be

Options

A. 40 minutes
B. 20minutes
C. 25 minutes
D. 30 minutes

Answer

A

Explanation

Let `N_(0)=100`
After 20% decay `N_(0)=80`
After 80% decay `N_(0)=20`
`N=N_(0)((1)/(2))^(n),(20)/(80)=((1)/(2))^(n)impliesn=2`.
`therefore` Required time`=2xx20=40` minute.