A Level Chemistry OCR Practice Exam

The definition of a hydrocarbon is best described as a compound consisting exclusively of hydrogen and carbon atoms. This is fundamental to the nature of hydrocarbons, which can be categorized into various types including alkanes, alkenes, and alkynes, based on their structure and the types of bonds present between the carbon atoms.

While the other options mention elements or characteristics related to compounds, they do not accurately capture what defines a hydrocarbon. For example, a compound of hydrogen and oxygen refers to substances such as water or hydrogen peroxide, which do not fit the hydrocarbon definition. Likewise, stating a hydrocarbon consists of carbon chains only does not account for hydrocarbons that can also contain branched chains or cyclic structures. Lastly, designating hydrocarbons as frequent byproducts of combustion describes a process in which hydrocarbons are involved, rather than defining what they are.