A radioactive sample has `6.0 xx 10^18` active nuclei at a certain instant. How many of these nuclei will still be in the same active state after two half-lives?

Options

A. `1 xx 10^(10)`
B. `5 xx 10^(9)`
C. `25 xx 10^(8)`
D. `5 xx 10^(8)`

Answer

C

Explanation

Number of nuclei remaining after n half lives `= (N_(0))/(2^(n))`
After 4 half life `= (N_(0))/(2^(4)) = (N_(0))/(16)` [as n= 4]
`= (4 xx 10^(10))/(16)= 25 xx 10^(8)`