The state in which a substance exists is generally controlled by which factor?

• A. Pressure
• B. Concentration
• C. Temperature
• D. Surface area

Answer: (C)

Temperature is what mainly sets the phase of a substance. At a given pressure, the amount of thermal energy (kinetic energy) of the molecules determines whether they are held tightly in place as a solid, can slide past each other as a liquid, or move freely as a gas. As you heat a material, it typically goes solid → liquid → gas, passing through melting and boiling points that mark those transitions. For example, water at atmospheric pressure is solid below 0°C, liquid between 0°C and 100°C, and gas above 100°C. Pressure can shift these boundaries, but the state is generally governed by temperature. Choices like concentration or surface area don’t determine whether a substance is a solid, liquid, or gas.