Carbon-dating is used to determine the age of -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Fossils
Carbon dating (radiocarbon dating) measures how much radioactive carbon-14 is left in the remains of something that was once alive. A living plant or animal keeps taking in carbon-14; after death the intake stops and the carbon-14 decays, halving about every 5,730 years. Comparing what is left with the amount in living matter gives the age, up to about 50,000 years, so it is used to date fossils and other organic remains such as bones, wood and charcoal.
Why the other options are incorrect
Option (1) Plants — Incorrect. A living plant still takes in carbon-14, so it has no age to measure; only its dead remains can be dated.
Option (3) Humans — Incorrect. The age of a living person is known; only ancient human remains, which are fossils and organic remains, are dated this way.
Option (4) Rocks — Incorrect. Rocks were never alive and are millions of years old; they are dated by other radioactive elements such as uranium and potassium.