A pure substance made of two or more elements chemically combined in a fixed ratio is called a?

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

Answer: (C)

When two or more elements join by chemical bonds in a definite proportion, they form a substance that has a fixed composition. That kind of substance is a compound. The fixed ratio means you’ll always see the same numbers of each type of atom in the formula, no matter how the material is prepared. Because the atoms are chemically bonded, compounds have properties that are different from the elements that make them up, and you typically need a chemical change to break them apart.

This differs from an element, which is just a single type of atom, and from a mixture, where substances are blended without chemical bonding and their proportions can vary; mixtures can usually be separated by physical methods. A molecule is a cluster of atoms held together, and it can be either a single-element molecule (like O2) or a compound molecule (like H2O). The phrase about two or more elements in a fixed ratio specifically describes a compound.