What ironic effect do details such as Zaroff's fine clothes expensive furnishings and knowledge of classical music have on the reader's impression of him?

These details create an ironic effect by portraying Zaroff as a sophisticated and cultured gentleman, which is contradictory to his true nature as a cold-blooded hunter who preys on human beings. The contrast between his refined appearance and his barbaric actions shocks the reader, highlighting the depth of his depravity.