What happens when a star exhausts its core hydrogen supply?
a. It contracts, becoming smaller and dimmer.
b It contracts, becoming hotter and brighter.
c. It expands, becoming bigger but dimmer.
d. Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
e. Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness.

d. Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

Explanation:

When the core runs out of hydrogen fuel, it will contract under the weight of gravity. ... The upper layers will expand and eject material that will collect around the dying star to form a planetary nebula. Finally, the core will cool into a white.

When a star exhausts the hydrogen in its core, it becomes a giant or supergiant. Once a star has used up all the hydrogen in its core, fusion of hydrogen into helium stops.

Answer is D. Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

Refer below.

Explanation:

The following happens when a star exhausts its core hydrogen supply:

Its core contracts, but its outer layers expand and the star becomes bigger and brighter.