A pure substance composed of multiple atoms chemically combined in a known ratio is called?

• A. Molecule
• B. Compound
• C. Element
• D. Mixture

Answer: (B)

The main idea is how a compound forms when different elements join together in a fixed, definite ratio. A compound is a pure substance that results when atoms of two or more elements bond chemically in a specific proportion, giving it new properties distinct from the constituent elements. The composition stays uniform throughout, which is what makes it pure. This differs from a mixture, where components are simply combined and can vary in ratio and are not bonded. A molecule is the smallest unit of a substance that retains its properties; it can be a diatomic element like O2 or a compound like H2O. So, a substance described as being composed of multiple atoms chemically combined in a known ratio is a compound.