Carbon-14 has a half-life of approximately 5,730 years. how many half-lives have occurred in a sample that contains 25 percent of the original amount of the parent isotope?

two half lives

Explanation:

half life is the time taken for the radioactivity of an isotope to reduce to half of its original value

therefore, in the first half life carbon-14 would have reduced by 50% in 5730 years

second half life, the isotope would have reduced to 25% in 11460 years

in three half lives, 12.5% of the isotope will be left after 17190 years, and so on

conclusively, 25% would remain after two half-lives have occurred

calculate how many grams of ammonia can be produced from 4.21 grams of

n2 + 3h2 = 2nh3

my answer:

25.0g n2 x (1 mol/ 28.0gn2) x (2 mol nh3/ 1 mol n2) x (17.0g nh3/ 1 molnh3) = 30.36g n2

25.0g h2 x (1 mol h2/ 2.00g h2) x (2 mol nh3/ 3 mol h2) x (17.0g nh3/ 1 mol nh3) = 141.67g h2

lr = n2

i'm assuming that the correct answer is indeed the first one/ "a"..