How do common alkanes differ from one another?

Common alkanes differ from one another primarily by the addition of a single –CH2– group, which illustrates how these hydrocarbon molecules grow in size and complexity. Alkanes are saturated hydrocarbons, meaning they consist entirely of carbon and hydrogen atoms with single bonds between them.

In the context of alkanes, as a carbon chain grows, each additional –CH2– unit represents a consistent increase in the number of carbon atoms while maintaining the chemical structure characteristics of alkanes. This addition creates a straight or branched chain of carbons, ultimately defining the identities of different alkanes such as methane, ethane, propane, and so forth.

While the other choices could relate to properties of alkanes in other contexts—like hydrogen content varying due to branching or molecular weight increasing with the number of carbon atoms—these variations do not specifically characterize how each alkane differs from the next in its simplest form. Functional groups, although relevant for other types of compounds, do not apply to alkanes as they are devoid of such groups. Therefore, the distinction among alkanes fundamentally lies in the incremental addition of the –CH2– units to their structure.