Which of the following is a type of biofuel?

Ethanol is classified as a type of biofuel because it is derived from the fermentation of plant materials, such as corn or sugarcane. Biofuels are renewable energy sources made from organic matter, and ethanol specifically is often used as a gasoline additive to reduce carbon emissions and improve fuel quality. Its production harnesses natural processes where biomass is converted into fuel, highlighting its sustainability potential compared to fossil fuels.

The other options represent different forms of energy. Propane is a petroleum-derived fuel and not a biofuel. Solar energy, while renewable, is generated from sunlight and does not involve biological sources in the same way that biofuels do. Nuclear energy is produced through nuclear reactions and involves the splitting of atoms, which is unrelated to biomass. Therefore, ethanol is the correct answer as it aligns with the definition and category of biofuels.