A Level Chemistry OCR Practice Exam

The term hydrocarbon refers specifically to a compound that contains only carbon and hydrogen atoms. This definition encompasses a wide variety of compounds, including alkanes, alkenes, and alkynes, which are all different types of hydrocarbons distinguished by their bonding and structural arrangements.

Hydrocarbons can be found in many substances, such as fossil fuels (like natural gas and petroleum), and they serve as a primary building block for many organic compounds. The absence of other elements in the definition of hydrocarbons makes the correct answer clear.

The other options describe compounds containing elements that are not part of the hydrocarbon definition. For instance, compounds consisting of carbon and nitrogen, or those that include oxygen and hydrogen alongside carbon, do not fit the hydrocarbon classification. Additionally, compounds formed from hydrocarbons and metals involve additional elements that go beyond the simplicity of a hydrocarbon's definition. Thus, the correct choice accurately captures the essence of what hydrocarbons are.