The activity of a radioactive element decreased to one - third of original activity `I_0` in 9 yr. After further 9 yr, its activity will be

Options

A. `R_(0)`
B. `(2)/(3)R_(0)`
C. `R_(0)//9`
D. `R_(0)//6`

Answer

C

Explanation

Since, `R= R_(0) e^(- lamda t)`
`(R_(0))/(3)= R_(0)e^(-9 lamda) rArr e^(-9 lamda) = 1//3`
Now, `R.= R e^(-9 lamda) rArr (R_(0))/(3) xx (1)/(3) (" as " R= (R_(0))/(3))`
`rArr R.= (R_(0))/(9)`