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. `1.5 xx 10^(18)`
B. `3 xx 10^(18)`
C. `6 xx 10^(18)`
D. None of these

Answer

A

Explanation

In one half-life the number of active nuclei reduces to half to original number. Thus in two half lives the number is reduced to `((1)/(2))xx((1)/(2))` of the original number. The number of remaining active nuclei is therefore.
`6.0 xx 10^(18) xx ((1)/(2))xx((1)/(2)) = 1.5 xx 10^(18)`.