The half-life of carbon-14 is 5,730 years. How many grams of parent material will remain from a 100-gram sample of carbon-14 after 2 half-lives?

75

6.25

12.5

25

The question is quite misleading at first because we are given the half life of the material. But the question is basically a simple geometric progression in which we need to multiply twice by 1/2 the initial amount since it is said that it has undergone 2 half lives.

therefore, after 2 half lives = 50 * 0.5 * 0.5 = 25