What is the fourth state of matter that is present in stars and fusion reactors?

The fourth state of matter that is present in stars and fusion reactors is plasma. Plasma is formed at extremely high temperatures when the energy is sufficient to strip electrons away from atoms, resulting in a collection of charged particles: ions and free electrons. This state of matter is characterized by its ability to conduct electricity and generate magnetic fields.

In stars, the immense gravitational forces and temperatures lead to conditions where hydrogen atoms fuse to form helium, releasing huge amounts of energy in the process. This fusion occurs in a plasma state, which is why stars are often referred to as giant balls of plasma.

In fusion reactors, scientists aim to replicate the processes that occur in stars by creating and sustaining plasma. This involves heating a gas (usually isotopes of hydrogen) to form plasma and then confining it using magnetic fields to achieve the conditions necessary for nuclear fusion.

Gas, while a state of matter that indeed exists, refers to particles that are not ionized and are simply moving freely around each other. Liquid refers to a state where particles are closely packed but can slide past one another, and solid relates to a state where particles are tightly bound in a fixed arrangement. None of these other states can conduct electricity or exist at the extreme temperatures found in stars and fusion reactors,