What is a compound?

A compound is defined as a substance that consists of two or more different elements that are chemically bonded together in fixed proportions. This means that a compound has a specific chemical formula, indicating the types and numbers of atoms involved. For example, water (H₂O) is a compound made up of hydrogen and oxygen atoms bonded together.

The key aspect that makes option C correct is the emphasis on chemical bonding between different elements, which distinguishes compounds from other forms of matter. In contrast, a pure substance that consists of only one type of element refers to an element, not a compound. A mixture combines two or more substances without chemical bonding, and an atom with a charge refers to an ion, which is not a compound but rather a charged species. Thus, option C encapsulates the essence of what a compound is within the context of chemistry.