Half life of a radioactive substance is 60 min. After 3 hours, the fraction of total number of atoms that have decayed would be

Options

A. `12.5%`
B. `87.5 %`
C. `8.5%`
D. `25%`

Answer

B

Explanation

t=3 hrs = 180 min
`t_(1//2)=60` min
`n=(t)/(t_(1//2))=(180)/(60)=3`
`N=(N_(0))/(2^(n))`
`N_(0)=100`
`N=(100)/(2^(3))=(100)/(8)=12.5`
`therefore` Total number of atoms decayed
`100-12.5 =87.5`