If `10%` of a radioactive material decays in `5` days, then the amount of original material left after `20` days is approximately.

Options

A. 0.6
B. 0.65
C. 0.7
D. 0.75

Answer

B

Explanation

(b) Disintegrating percentage `= 10`
Surviving percentage `= 100 - 10 = 90`
Surviving fraction `=f`
`f = (90)/(100) = 0.9`
`t_f = 5 days t = 20 days`
`n_f = (t)/(t_f) = (20)/(5)= 4`
`(N)/(N_0) = (f)^(n_f) = (0.9)^4`
` :. ((N)/(N_0)) xx 100 = 0.6560 + 100`
`=65.6 %`.