A compound composed of two elements is called what?

A compound composed of two elements is called what?

• A. Polyatomic ion
• B. Binary compound
• C. Ternary compound
• D. Ion molecule

Answer: (B)

A compound composed of two elements is called a binary compound. Binary means two, so this term applies to any substance formed when exactly two different elements join together, whether the bond is ionic or covalent. Examples include sodium chloride (NaCl), carbon dioxide (CO2), and water (H2O)—each has two elements in its formula. The other terms don’t fit because a polyatomic ion refers to a charged group of atoms, not just two elements in a neutral compound; a ternary compound contains three different elements; and “ion molecule” isn’t a standard way to describe a two-element compound.

A compound composed of two elements is called a binary compound. Binary means two, so this term applies to any substance formed when exactly two different elements join together, whether the bond is ionic or covalent. Examples include sodium chloride (NaCl), carbon dioxide (CO2), and water (H2O)—each has two elements in its formula.

The other terms don’t fit because a polyatomic ion refers to a charged group of atoms, not just two elements in a neutral compound; a ternary compound contains three different elements; and “ion molecule” isn’t a standard way to describe a two-element compound.