Question

What is the next step in the sun's life cycle after it has used up its hydrogen fuel.

Answer 1

I believe the Sun will become a C. Red Giant.
When a star uses up its hydrogen fuel, it starts getting cooler and cooler, but also much much bigger. When our Sun becomes a Red Giant, it will become many times larger than it is now, but as its temperature goes down it will turn its color from yellow to red or orange. In time, it will either become a White Dwarf or create a black hole.