What is the primary composition of a hydrocarbon?

The primary composition of a hydrocarbon consists solely of hydrogen and carbon. This definition is fundamental to understanding hydrocarbons, which are organic compounds primarily made up of these two elements. The simplest hydrocarbons are alkanes, such as methane (CH₄), which is made up of one carbon atom and four hydrogen atoms. The structure and properties of hydrocarbons are determined by the number of carbon and hydrogen atoms present.

When considering the other options, it's important to note that while oxygen may be involved in some organic compounds (e.g., alcohols, carboxylic acids), it is not part of the defining structure of hydrocarbons. Nitrogen, while present in some organic and inorganic compounds, does not belong to the standard definition of hydrocarbons either. Chlorine is sometimes associated with halogenated hydrocarbons but is not a constituent of basic hydrocarbon structures. Therefore, focusing on the correct elements involved in hydrocarbons is crucial for accurate identification and understanding of their chemical nature.