9. Assume you began with 10 g of a radioactive parent isotope. How many grams of parent isotope will be present in the same sample after 2 half-lives?

A. 5.0 g
B. 2.5 g
C. 1.25 g
D. 0.63 g

Is it A???

2 answers

no, 5 is 1/2 of 10, so that is what's left after one half-life
You want half of that.
Okay, thank you.