What is 14c used for?

Answer 1

labelling of molecules, so you can se where the molecule is going into the plant or animal, from a radioanalysis of the tissues.

Determining the age of an organic object, because 14C is not stable and the % in living organism is stable, when an organism die 14C diminish and you can measure the remaining and say how many years it has
14C datation is accurate only until 35000 years.

Willard Franck Libby took the nobel in 1960 for radiodatation with 14C