The activity of a radioactive samples reduces by 10% in 12.5 yr. The half-life of this radioactivity species when it is reduded to 90% .

Options

A. 28.20 yr
B. 82.20 yr
C. 2.5 yr
D. 12.5 yr

Answer

B

Explanation

Half-life of a species remains constant. `N = (N_(0) xx 90)/(100)`
Now `lambda = (2.303)/(12.5) log "" ( 100)/(90) = 8.43 xx 10^(-3) " " therefore t_(1//2) = (0.693)/(8.43 xx 10^(-3)) = 82.20` yrs