The acitivity per ml of a solution of radioactive substances is x. How much of water be added to 200 ml of this solution so that the acitivity falls to `x//20` per ml after 4 half-lives ?

Options

A. 100 ml
B. 150 ml
C. 80 ml
D. 50 ml

Answer

D

Explanation

`N=N_0(1/2)^n`
let the volume of final solution be V ml.So activity after 4 half lives =`x/20 xxV`
Initial activity =`x xx 200`
`((xV)/20)=(x xx20)(1/2)^4`
V=250 ml
So added volume of water =50 ml