Which of the following describes a compound? (hint: carbon and oxygen both appear on the periodic table.) a. a piece of pure carbon, containing only carbon atoms b. oxygen gas surrounding a solid piece of carbon c. a substance made of two oxygen atoms for each carbon atom d. carbon and oxygen atoms mixed without being bonded together

Compound is defined as a pure substance which is made up of two or more different elements present in the fixed ratio and they can be separated into smaller substances by means of chemical processes.

Thus, a substance made up of two oxygen atoms for each carbon atom describes a compound as the substance is made up of two different elements which are present in the fixed ratio.

Hence, option c that is a substance made up of two oxygen atoms for each carbon atom describes a compound.

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the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.