Question

Two radioactive `X_(1)` and `X_(2)` have decay constants `10 lambda ` and `lambda` respectively . If initially they have the same number of nuclei, then the ratio of the number of nuclei of `X_(1)` to that of `X_(2)`will be `1//e` after a time .
A. `1//(10 lamda)`
B. `1//(11 lamda)`
C. `11//(10 lamda)`
D. `1//(9 lamda)`

Answer 1

Correct Answer - D
`N_(1)=N_(0)e^(-10 lamda t)` and `N_(2)=N_(0)e^(-lamdat)`
`rArr (N_(1))/(N_(2))=(1)/(e)=e^(-1)=e^((-10 lamda+lamda)t)=e^(-9 lamda t) rArr t = (1)/(9 lamda)`.