Penn Foster Biology – The Cell Practice Test 2026 - Free Biology Practice Questions and Study Guide

The three primary phases in which matter can exist are solid, liquid, and gas. These states are defined by the arrangement and behavior of molecules within the matter.

In the solid state, molecules are closely packed together and vibrate in place, giving solids a definite shape and volume. Liquids have molecules that are more loosely arranged than in solids, allowing them to flow and take the shape of their container while maintaining a fixed volume. Gases consist of molecules that are far apart and move freely, resulting in no fixed shape or volume, as they expand to fill their container.

Understanding these fundamental states of matter is crucial in various fields of science and helps explain phenomena observed in nature and everyday life. The other options include phases like plasma, which is less commonly recognized as a primary state in basic discussions, or concepts like energy and light that are not molecular states of matter.