What term describes a region of uniform properties within a material system?

• A. Phase
• B. State of a Substance
• C. Change of State
• D. Intensive Property

Answer: (A)

A phase is a region of uniform properties within a material system. It represents a distinct, homogeneous portion of matter where properties such as composition, temperature, and density are uniform throughout, and it is separated from other regions by a phase boundary. For example, water can exist as a liquid phase and a vapor phase at the same time under the right conditions; each phase has uniform properties within it, while different phases have different properties.

This is different from the state of a substance, which describes its overall condition (solid, liquid, or gas) rather than a spatial region within the system. A change of state refers to the transition between phases, such as melting or boiling. An intensive property is a type of property that does not depend on the amount of material, like temperature or pressure, and it isn’t a term for a region of uniform properties.