What is a combination of two or more elements bonded together?
A compound is a combination of two or more elements that are chemically bonded together in a fixed whole number ratio. A mixture is composed of two or more substances (elements or compounds) mixed together, but not chemically bonded to one another and are generally not in a fixed ratio. Unlike a compound, the components of a mixture can be separated by physical means.
Carbon Dioxide (CO2). Compounds tend to be made from 2 or more different elements bonded together either covalently or ionically. They are all made of 2 or more elements bonded together whether those elements are the same or not. The other options are elements (Fe, O, and Ca respectively). They are not bonded to anything and therefore do not make a compound.
Substances composed of two or more elements bonded together in definite proportions are chemical compounds by definition. This is not a correct definition for minerals, because some of them are mixtures of more than one compound, and some minerals, such as gold and diamond, are elements instead of compounds.