The correct statement is:
Carbon dating is used for absolute dating, but index fossils are not.
Carbon dating (radiocarbon dating) is a method used to determine the age of organic materials by measuring the decay of carbon-14 isotopes, allowing for absolute dating of materials up to about 50,000 years old. In contrast, index fossils are used in relative dating, where they help establish the relative ages of rock layers and the fossils within them based on the known time ranges in which those species existed.