A radioactive substance has a half life of `60` minutes. After `3` hours, the fraction of atom that have decayed would be.

Options

A. `17.5%`
B. `12.5%`
C. `25%`
D. `50%`

Answer

B

Explanation

`N_(0)=100`
N=?
`t_(1//2)=60` min
Total time =3 hours
No. of half lives, `n=(180)/(60)=3`
`N=[(1)/(2)]^(n)xxN_(0)`
`N=((1)/(2))^(3)xx100=(1)/(8)xx100`
12.5%