When the core of a star like the sun uses up its supply of hydrogen for fusion, the core begins to

Shrink and heat

Explanation:

Hope my answer has helped you!

Shrink and heat up

Explanation:

When the core of a star like the Sun uses up its supply of hydrogen for fusion, the core begins to contract or shrink up which leads to release of energy from the core.

The released energy starts to heat up core until it has gotten to the point where the core is hot enough to able start up the fusion of hydrogen into another element (helium).

The layers on the outside of the sun absorbs the released the energy and starts to enlarge or swell up and the sun develops a very high luminosity which means it start to shine brighter and brighter.

As the outside large swells up, due to the absorption of the released energy, it start to become cool thereby causing a low surface temperature.

It is at the stage that the sun becomes a red giant.

d. air pressure decreases as altitude increases.