Substances composed of combinations of two or more different atoms are known as

• A. elements.
• B. compounds.
• C. isotopes.
• D. mixtures.

Answer: (B)

Two or more different elements bonded together form a compound. In a compound, atoms are held together by chemical bonds in a fixed ratio, and the compound as a whole has properties that are usually very different from its constituent elements. You must break chemical bonds to separate a compound into its components, which typically requires a chemical reaction. This differs from elements, which are pure kinds of atoms; isotopes, which are the same element with different neutron counts; and mixtures, where components are simply combined without bonding and can be separated by physical means. For these reasons, substances made from two or more different atoms in a definite composition are called compounds.