Answer:
Carbon - 14
Step-by-step explanation:
Carbon-14 dating is the technique to find out the age of biological samples like bones and wood. Carbon-12 is usually present in cells and forms the basis of organic substances. But occasionally a carbon-14 atom also gets incorporated. When energetic neutrons in atmosphere hit nitrogen-14 atom, it gets converted to carbon-14 atom. This carbon-14 is taken up by plants in form of carbon dioxide during photosynthesis and taken up by animals when they eat them.
Ratio of carbon-12 ( normal carbon ) to carbon-14 is constant in a living organism. But when an organism dies, it stops taking up new carbon and carbon-14 starts to decay because it is unstable thus changing the ratio. The ratio in the sample is compared to the ratio in living organisms to give an estimated age of the sample.