Which is true of a radioisotope that is used to date rock formations? It has a long half-life. It is a plentiful isotope. It has a short half-life. It is a rare isotope.

The method that uses radio isotope to date rock formation is called radiometric dating or radioactive dating. This is to determine the age of the rocks. In this technique, the decay rate of the isotopes serves as the basis. Therefore, the answer that shows the true statement of a radio isotope is this: it has a long half-life.