Petroleum-based fuels are hydrocarbons, which means they are:

• A. They are inorganic compounds.
• B. They are polar solvents.
• C. They are polymers.
• D. They are hydrocarbons.

Answer: (D)

Petroleum-based fuels are hydrocarbons because they are organic compounds made entirely of hydrogen and carbon. This means the molecules are nonpolar and consist of chains or rings of carbon with attached hydrogen, typical of many fuels. They are not inorganic compounds, since those lack the carbon-hydrogen makeup. They are not polar solvents—hydrocarbons are generally nonpolar and don’t mix well with water. They aren’t polymers, which are large, repeating-unit macromolecules; fuels are mixtures of smaller hydrocarbon molecules, not long-chain polymers.