Why do lipid-rich foods become rancid when exposed to oxygen for too long

Fats and oils that are in contact with moist air at room temperature eventually undergo oxidation and hydrolysis reactions that cause them to turn rancid, acquiring a characteristic disagreeable odor. One cause of the odor is the release of volatile fatty acids by hydrolysis of the ester bonds.

Explanation:

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

oxygen +1 most likely