Final answer:
Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen atoms, and they are classified as lipids. They vary in structure and are commonly found in fuels and plastics.
Step-by-step explanation:
The hydrocarbons are a type of organic compound, and in the context of the student's question, the correct answer is that hydrocarbons fall into the category of lipids. These substances are composed exclusively of carbon (C) and hydrogen (H) atoms. Hydrocarbons can be found in various forms, such as aliphatic hydrocarbons, which consist of chains or rings of carbon atoms, and aromatic hydrocarbons that include planar ring structures. Hydrocarbons are ubiquitous in daily life, being major constituents in fuels, plastics, and natural deposits. They vary based on the length and structure of their carbon chains, and the type of carbon-carbon bonds, which can be single, double, or triple within the molecules. The plastics mentioned by the student, like polyethylene and polypropylene, are commercial examples of aliphatic hydrocarbons.