Final answer:
Linoleic acid is an unsaturated fatty acid due to the position of the first C=C bond in the nonpolar chain. This double bond creates a kink in the chain, making the fatty acid liquid at room temperature.
Step-by-step explanation:
Linoleic acid is called an unsaturated fatty acid because of the position of the first C=C in the nonpolar chain. Unlike a saturated fatty acid that has all single bonds between carbon atoms, linoleic acid has double bonds between certain carbon atoms. This double bond causes a kink in the chain, preventing the fatty acid molecules from packing together tightly and making them liquid at room temperature.