Molecular Theory explains the behavior of matter at the molecular level. It states that all matter is made up of tiny particles called molecules, which are in constant motion. The energy of these molecules affects their speed and interactions, influencing the state of matter—solid, liquid, or gas. According to this theory, temperature is a measure of the average kinetic energy of the molecules. As temperature increases, molecules move faster, leading to changes in physical properties. This theory helps to understand various phenomena, such as diffusion, phase changes, and the behavior of gases described by gas laws.