When the sun finishes its red giant phase, it will become a white dwarf, a small and dense star remnant. Our sun is a medium-sized star, and after it runs out of fuel, it expands into a red giant. During this phase, the sun’s outer layers swell up enormously, and it will lose some of its mass by blowing off gas into space.

Eventually, the sun cannot hold its outer layers anymore, and these layers drift away, leaving behind the hot core. This core cools and shrinks to become a white dwarf. White dwarfs are very dense — about the size of Earth but with the mass of the sun — and they no longer produce energy by fusion.

Here’s why the other answers are incorrect:
- **Supernova**: This is an explosive end for very massive stars, not for stars like the sun.
- **Black hole**: Only stars much bigger than the sun become black holes.
- **Neutron star**: Like black holes, neutron stars come from very massive stars after supernova explosions.

The white dwarf stage is the final phase for stars like the sun, and it will slowly cool over billions of years. Understanding this process helps us learn about the future of our solar system and similar stars in the universe.

So, the correct answer is **White Dwarf** — the quiet and dense star left after the sun’s red giant phase.