Chemistry

Question Analysis
This question involves the classification of matter and its relationship to state changes.
The main focus is on identifying which category of matter can undergo transitions between the three common states.

Key Concept Explanation
Pure substance: A substance with a fixed composition (either an element or a compound) that can exist in solid, liquid, or gas states depending on temperature and pressure (e.g., water: ice, liquid water, water vapor).
Mixture: A combination of two or more pure substances; while mixtures can change state, the term does not describe the ability to exist in three states—it describes composition.
Element/Compound: Subtypes of pure substances; while they can exist in three states, the question asks for the broader term that includes both.
All elements and compounds are pure substances, but not all pure substances are elements

Step-by-Step Solution
1. Eliminate Option B (Mixture)—mixtures are defined by their composition (multiple sub...