Which of the following represents an alkane?

An alkane is a type of hydrocarbon that consists exclusively of single bonds between carbon atoms and follows the general formula CnH2n+2, where n is the number of carbon atoms.

In this case, the given formula C5H12 classifies it as an alkane. It contains five carbon atoms (n=5), and applying the alkane formula yields C5H(2(5)+2) = C5H12. This matches the structure of C5H12, confirming that it is indeed an alkane.

The other compounds do not fit the definition of alkanes. For example, C3H6 and C4H8 are unsaturated hydrocarbons, as indicated by their lower hydrogen count than what would be expected for alkanes with three and four carbons, respectively. C2H4 is also unsaturated and represents an alkene due to the presence of double bonds. Thus, these compounds cannot be classified as alkanes.