Concept: The correct preposition is the one used in the fixed expression “too much of a/an...”.Explanation:The phrase “too much of” is a standard English structure.It is used before a singular noun to describe a person's quality.For example: “He is too much of a coward to try.”Here, “an idealist” is a singular noun phrase, so “of” is required.Thus, the completed sentence is: “The chairman is too much of an idealist for coming late.”Answer: D. Of.