Which of the following causes a substance to change its state of matter from a solid to a liquid?

• A. Increasing the temperature above the melting point
• B. Decreasing the temperature below the freezing point
• C. Increasing the pressure at constant temperature
• D. Decreasing the pressure below the triple point

Answer: (A)

Verified step by step guidance

1. Understand that changing the state of matter from solid to liquid is called melting.
2. Recall that melting occurs when a solid absorbs enough heat to reach its melting point, causing its particles to gain energy and move more freely.
3. Recognize that increasing the temperature above the melting point provides the energy needed for the solid to overcome the forces holding its particles in a fixed position, thus becoming a liquid.
4. Note that decreasing the temperature below the freezing point causes a liquid to become a solid (freezing), which is the opposite process.
5. Understand that changing pressure can affect states of matter, but increasing pressure at constant temperature usually favors the solid phase, and decreasing pressure below the triple point can lead to sublimation rather than melting.