A sample of radioactive element has a mass of `10 g` at an instant `t=0`. The approximate mass of this element in the sample after two mean lives is

Options

A. 2.50 g
B. 3.70 g
C. 6.30 g
D. 1.35 g

Answer

D

Explanation

`N= N_(0) e^(- lamda t) rArr M = M_(0) e^(-lamda t)`
`t= (2)/(lamda) = 2tau`
`therefore M= 10 e^(-lamda ((2)/(lamda)))= 10 ((1)/(e))^(2) rArr M= 1.35g`