A binary compound is defined as which of the following?

• A. a compound formed from two molecules
• B. a compound composed of two elements
• C. a mixture of two elements
• D. a molecule with two atoms of the same element

Answer: (B)

A binary compound is a chemical substance formed when two different elements are chemically bonded in a fixed ratio. This means the compound has two elements in its makeup, not just a mixture of elements and not a molecule consisting of only one element. The idea is that the elements are chemically joined to create a single substance with a definite composition, as in water (two elements, hydrogen and oxygen) or sodium chloride (two elements, sodium and chlorine). So describing it as a compound composed of two elements best captures that two different elements are chemically united in a definite ratio.