The correct option is D Oleic acid
Stearic acid is a saturated fatty acid with 18 carbon atoms.
Palmitic acid is a saturated fatty acid with 16 carbon atoms.
Arachidonic acid is a saturated fatty acid with 20 carbon atoms.
Oleic acid is a monounsaturated fatty acid (MUFA). It means the structure of oleic acid has 1 unsaturated double bond between carbon atoms.