Answer:
A stylish cap
Explanation:
A prepositional phrase is a group of words that consists of a preposition, its object, and words that modify the object. The preposition used in the given sentence is for. Its object is graduation, and his is the word that modifies the object.
This phrase modifies (describes) the noun phrase a stylish cap. It's a cap made for a special occasion, a stylish cap made for Richard's graduation.
