Question

what will a medium - mass star become at the very end of its life cycle?
a red giant
a black hole
a black dwarf
a neutron star

Explanation:

A medium - mass star (with a mass between about 0.5 and 8 times the mass of the Sun) goes through several stages. First, it is a main - sequence star (fusing hydrogen in its core). Then it becomes a red giant (fusing helium in a shell around the core). After shedding its outer layers (forming a planetary nebula), the core remains. For a medium - mass star, this core cools down over time and becomes a black dwarf. A red giant is an intermediate stage, not the end. A black hole is formed from very massive stars (more than about 20 times the Sun's mass). A neutron star is formed from stars with a mass in the range of 8 - 20 times the Sun's mass (after a supernova explosion).

Answer:

a black dwarf