Which term describes matter that is a single type of substance with fixed properties and composition?

• A. Heterogeneous mixture
• B. Pure substance
• C. Compounds
• D. Particles

Answer: (B)

A pure substance is matter with a single type of material and fixed composition, giving it uniform properties throughout. This means it can be an element (like oxygen) or a compound (like water), where the proportions of the constituents are fixed. The description in the question fits this idea because it emphasizes a single substance with definite properties and composition. A heterogeneous mixture would not be uniform in composition, and while a compound is a pure substance, the broader term that covers all one-substance cases is pure substance.