A saturated hydrocarbon is defined as which of the following?

• A. A hydrocarbon containing at least one double bond
• B. A hydrocarbon in which all bonds between carbon atoms are single bonds; completely saturated with hydrogen
• C. A hydrocarbon with aromatic rings
• D. A hydrocarbon with at least one heteroatom

Answer: (B)

Saturation refers to how many hydrogen atoms can bond to the carbon skeleton given the bonds between carbon atoms. If every carbon–carbon bond is a single bond, each carbon can use its valence to bond to the maximum number of hydrogens. That results in a hydrocarbon that is fully saturated with hydrogen, which is the hallmark of alkanes (and cycloalkanes) with formulas like CnH2n+2 (open chains) or CnH2n (rings).

That description matches the statement that all carbon–carbon bonds are single bonds and the compound is completely saturated with hydrogen.

The other descriptions don’t fit: a double bond or aromatic ring implies unsaturation with fewer hydrogens than the saturated case due to pi bonding; and a heteroatom would mean the substance is not a pure hydrocarbon at all.