Which word describes the act of deriding or treating with contempt?

The word that describes the act of deriding or treating someone with contempt is "derision." This term specifically denotes a feeling or expression of contemptuous ridicule or scorn. When someone treats another person with derision, they are belittling or mocking them, which aligns perfectly with the concept of treating others with disdain.

In contrast, the other choices do not convey this meaning at all. Appreciation refers to recognizing the value or quality of something positively, affection denotes a gentle feeling of fondness or liking, and admiration involves respect and warm approval. Each of these terms centers around positive or neutral feelings, which contrasts sharply with the negative connotation of derision. Thus, "derision" stands out as the only term that encapsulates the act of mocking or showing contempt.