Question

which of the stars is the oldest?
red giant
main sequence
white dwarf
all are the same age

Explanation:

A star's life cycle progresses from the main - sequence stage. After exhausting nuclear fuel, it expands into a red giant. Finally, it collapses to form a white dwarf. So, white dwarfs are the remnants of older stars that have completed most of their life cycle stages.

Answer:

White dwarf