It would be "b. Benito Mussolini" who was the fascist leader known as Il Duce, since this is Italian for "the Leader," and Mussolini had almost complete control of the Italian state.
The fascist leader who was known as II Duce was Benito Mussolini- B. Mussolini was the leader of fascist Italy in pre-war and during the war. During World War II that is.
