Carbon dioxide is c) a compound. It is formed when one carbon atom bonds with two oxygen atoms, resulting in the chemical formula CO2.
To explain further, a compound is a substance that is made up of two or more different elements that are chemically bonded together. In the case of carbon dioxide, the carbon element and the oxygen elements combine through covalent bonds, which means they share electrons.
On the other hand, an element is a pure substance that cannot be broken down into simpler substances, while a mixture involves two or more substances that are not chemically bonded and can be separated. Since carbon dioxide has a definite composition and distinctive properties that differ from its constituent elements, it is classified as a compound.