Which statement is true about the state of matter?

• A. The classical states are solid, liquid, and gas
• B. There are four equally common states
• C. Plasma is never considered a state of matter
• D. Gas is the only state that can change phase

Answer: (A)

Understanding how matter is categorized helps answer this. The true statement is that the classical states are solid, liquid, and gas. These three categories describe most everyday situations: solids keep their shape and volume, liquids keep their volume but take the shape of their container, and gases have neither a fixed shape nor a fixed volume.

Plasma is often taught as a fourth state of matter, produced when a gas is energized enough to ionize. So saying plasma is never a state of matter isn’t accurate. There are other less common or more exotic states as well (like Bose-Einstein condensates at very low temperatures), though they aren’t part of the everyday three.

The idea that there are four equally common states isn’t supported by typical science education, and the claim that gas is the only state that can change phase is false. Solids can melt, liquids can freeze or vaporize, and gases can condense under the right conditions.