A radioactive sample has `8.0xx10^(18)` active nuclei at a certain instant. How many of these nuclei will still be in the active state after two half-life `("in" xx10^(18))`?

Answer

2

Explanation

In one half-life the number of active nuclei reduces to half the original number. Thus, in two half-lives the numbers is reduced to `((1)/(2))((1)/(2))` of the original number. The number of remaining active nuclei is, therefore,
`8.0xx10^(18)xx((1)/(2))=2xx10^(18)`.