Which of the following refers to a fixed false belief?

A fixed false belief is best described by the term “delusion.” Delusions are characterized by a strong conviction in beliefs that are not grounded in reality and persist despite evidence to the contrary. This can manifest in various forms, such as paranoid delusions, grandiose delusions, or somatic delusions, but they all share the common feature of being firmly held beliefs that are resistant to change.

In contrast, hallucinations involve sensing things that are not present, like hearing voices or seeing things that aren't there, making it distinct from the concept of a delusion. Mutism refers to a lack of speech, often in specific contexts, and does not relate to beliefs. Narcissistic typically describes a personality trait or disorder characterized by a pervasive pattern of grandiosity, need for admiration, and lack of empathy, rather than a specific type of belief. Therefore, “delusion” is the most appropriate term for a fixed false belief.