After 3 half lives of a radioactive substance remains A al B one half C one third D one eighth?
After 3 half lives, the original substance will be reduced by a factor of 2 each time.
So after the first half-life, it will be reduced to half (A al B). After the second half-life, it will be reduced to one-quarter (A al C). After the third half-life, it will be reduced to one-eighth (A al D).