# Which is the unsaturated acid: "A. diacetic acid; B." H_3C(CH_2)_14CO_2H; "C. oleic acid; D. arachidic acid?"

Only $C .$ is an unsaturated acid.
An unsaturated carboxylic acids contains only the ${1}^{\circ}$ of unsaturation. For instances, $\text{acetic acid}$, $\text{H"_3"CC(=O)OH}$, has formula ${C}_{2} {H}_{4} {O}_{2}$, i.e. ${1}^{\circ}$ of unsaturation.
Both $\text{palmitic}$, and $\text{butyric acids}$ are saturated by this definition. $\text{Palmitic acid}$, i.e. palm oil, is the typical saturated fatty acid, and this is the food component that nutritionists encourage us to avoid.
On the other hand $\text{oleic acid}$, ${C}_{18} {H}_{34} {O}_{2}$, is the typical UNSATURATED acid (and cis with respect to the necessary double bond), that is found in olive oil, and which nutritionists promote.