Which of the following terms describes a star that has entered a later stage of development characterized by expansion and fusion of heavier elements?

The term that describes a star that has entered a later stage of development characterized by expansion and fusion of heavier elements is a supergiant. In this stage, the star has exhausted its core hydrogen fuel and has expanded significantly in size. During this phase, the core temperature rises, enabling the fusion of heavier elements beyond hydrogen and helium, such as carbon, neon, and even iron in some cases.

Supergiants are enormous stars—often many times larger than the Sun—and showcase powerful stellar phenomena. Their lifespans in this phase are relatively short on an astronomical timescale, as they rapidly use up their fuel and undergo various processes leading to their eventual fate, whether that be a supernova explosion or another end-of-life scenario.

In contrast, terms like neutron star and black hole refer to remnants of stars that have gone through their life cycles and are in much denser states. A protostar, on the other hand, is an early stage in a star's formation that has not yet begun nuclear fusion. Thus, supergiant accurately encompasses the characteristics of a star in this advanced stage of stellar evolution.