Question

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?

Answer 1

If 25% is remaining, two half lives have occurred.

After one half life, 50% remains. The after a second, 25% remains

Hope this helps

Answer 2

two half lives

Step-by-step 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