Which of the following is not a state of matter?

The correct answer identifies that the plasma state is indeed a state of matter. Matter typically exists in several states, including solid, liquid, gas, and plasma.

Plasma is recognized as a distinct state of matter that occurs at extremely high temperatures, where gas is energized to the point that electrons are stripped from their atoms, resulting in a collection of charged particles. In this state, plasmas are found in places such as stars, including the sun, where the extreme conditions allow this state to exist.

In contrast, the other options—solid, liquid, and gas—are more familiar states of matter that we encounter commonly in everyday life. Solids have fixed shapes and volumes, liquids have definite volumes but take the shape of their container, and gases neither have fixed shapes nor volumes, expanding to fill any available space.

Recognizing plasma as a valid state of matter reinforces the understanding that there are several forms in which matter can exist, all characterized by differing properties based on temperature and energy levels.