When thermal energy in a solid is increased, the change in state is called

Analysis

The question asks for the specific term used to describe the phase change that occurs when a solid substance absorbs thermal energy (heat) until it transitions into a liquid state.

Concept Explanation

In thermodynamics, matter exists in different states (solid, liquid, and gas). These states are determined by the kinetic energy of the molecules.

• Solid: Molecules are tightly packed and vibrate in fixed positions.
• Thermal Energy: When you add heat to a solid, the kinetic energy of the molecules increases, causing them to vibrate more vigorously.
• Phase Change: Eventually, the energy becomes sufficient to overcome the intermolecular forces holding the solid structure together. The solid begins to lose its rigid shape and turns into a liquid. This process is known as melting (or fusion).

Let's look at the other options to understand why they don't fit:

• Evaporation: This is the change from a liquid to a gas.
• Freezing: This is the change from a liquid to a solid (this happens when thermal energy is removed, not increased).
• Condensation: This is the change from a gas to a liquid.

Step-by-Step Solution

1. Identify the starting state: The question specifies a "solid."
2. Identify the process: The question specifies that thermal energy is "increased."
3. Determine the result: Increasing the temperature of a solid leads to the breaking of its lattice structure, resulting in a liquid.
4. Match with terminology: The scientific term for the transition from solid to liquid is melting.

Conclusion

Based on the principles of thermodynamics, when a solid is heated to its melting point, it undergoes a phase change into a liquid. Therefore, the correct term is melting.

Exam Tip: Always remember the direction of heat flow. If heat is added, the substance moves "up" the energy scale (Solid → Liquid → Gas). If heat is removed, the substance moves "down" the energy scale (Gas → Liquid → Solid).