Final answer:
The term for someone who contrasts or challenges another character is a 'Foil'.
Step-by-step explanation:
The term for "someone who serves as a contrast or challenge to another character" is C) Foil. A foil is a character who emphasizes the traits of a main character, usually the protagonist, through contrast by being their opposite in many ways. Authors often use foils to highlight a protagonist's characteristics or to underscore their development throughout the narrative. For instance, a decisive and ambitious foil could be used to accentuate a protagonist's hesitancy or lack of direction. Hence, among the given options, option c) Foil is the term for someone who contrasts or challenges another character