An accident occurs in a laboratory in which a large amount of a radioactive material, having a half life of `20` days, becomes embeded in the foor and walls so that the level of adiation is `32` times the permissible level. The laboratory can be safely occupied after

Options

A. `20` days
B. `32` days
C. `64` days
D. `100`days

Answer

D

Explanation

`A = A_(0)((1)/(2))^(n)`
`(A)/(A_(0)) = (1)/(32)= ((1)/(2))^(n) rArr ((1)/(2))^(5) = ((1)/(2))^(n) rArr n = 5`
`t = nT_(1//2) = 5xx20 = 100days`