Question

if there were 100 mg of carbon-14 in a sample 11460 years ago, how much would there be present day?

Answer 1

Answer : 25 mg

The half-life of a radioactive isotope is the time taken for half of the isotope to decay in a given sample . The half-life of carbon 14 isotope is 5,730 years.

Halft life of C-14 isotope is 5730 years, which means that a given quantity of C-14 isotope will decay to half the quantity in a period of 5730 years.

So, 100 mg of C-14 decays to ----------------------> 50 mg in 5730 years  

50 mg of C-14 decays to -------------------> 25 mg in next 5730 years

So, at the end of 11460 yeras ( 2 half-lives), 25 mg of C-14 isotope will be left.