Which one of the following acids is most abundant in fats and oils from plants and animals?

Stearic acid is the most abundant fatty acid found in both plant and animal fats and oils. It is a saturated fat with a long carbon chain, specifically consisting of 18 carbon atoms. This structure contributes to its solid-state at room temperature and is a significant component of various dietary fats.

In the context of dietary fats, stearic acid plays a role in energy storage and metabolic processes, making it an important acid in nutrition and biochemistry. It is commonly found in animal fats, cocoa butter, and certain vegetable oils.

On the other hand, the other acids listed—citric acid, acetic acid, and formic acid—are not primarily associated with fats and oils. Citric acid is mainly found in citrus fruits and is known for its role in the citric acid cycle in metabolism. Acetic acid is primarily found in vinegar and plays a role in various industrial applications rather than contributing to the fat profile of oils and fats. Formic acid, on the other hand, is more commonly associated with certain insects and is not a significant component in dietary fats.

Thus, stearic acid stands out as the main fatty acid relevant to fats and oils, making it the correct choice for this question.