Final answer:
The concept of degenerate matter relates to a star's core being supported by degeneracy pressure, leading to it becoming a white dwarf for stars less than about 1.4 solar masses. For more massive stars, degeneracy occurs but is ultimately followed by a collapse into a neutron star or black hole.
Step-by-step explanation:
The term 'degenerate matter' in the context of star death refers to a state where the core of a star is supported by pressure arising not from thermal energy, but from quantum mechanical effects. When a star's core stops nuclear fusion and becomes degenerate matter, for stars less than about 1.4 solar masses, it becomes a white dwarf. For more massive stars, although the onset of degeneracy occurs, their core eventually collapses under gravity to become either neutron stars, if above 1.4 but below about 3 solar masses, or black holes if the mass is greater than around 3 solar masses. In this way, degenerate matter allows a star to achieve a state of equilibrium as a white dwarf.
Option C: 'When a star's core becomes degenerate matter' is the correct answer to the student's question, as it describes the state in which a star's core is supported by degeneracy pressure from the electrons within, which resist being squeezed into the same quantum state.