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 (like the Sun) first becomes a red giant. After shedding its outer layers, it leaves behind a white dwarf. As the white dwarf cools over a very long time (trillions of years), it becomes a black dwarf. A black hole is formed from the collapse of a very massive star (much more massive than a medium - mass star). A neutron star is also formed from the collapse of a more massive star (typically 8 - 20 times the mass of the Sun).

Answer:

a black dwarf