What are the two categories of flammable liquids?

• A. Hydrocarbon fuels and water
• B. Hydrocarbon fuels and polar solvents
• C. Polar solvents and water
• D. Gas and liquids

Answer: (B)

Flammable liquids are classified by the chemistry of their molecules, which affects how easily they form ignitable vapors. The two common categories are hydrocarbon fuels, which are nonpolar carbon–hydrogen liquids like gasoline and mineral spirits, and polar solvents, which are liquids with polar molecules such as acetone, methanol, and ethanol. Both groups have relatively low flash points and can produce ignitable vapors under normal conditions. Water isn’t flammable, so it doesn’t belong in these categories, and calling something a gas and a liquid isn’t about flammability of liquids. That’s why grouping flammable liquids as hydrocarbon fuels and polar solvents is the best answer.