Option 1: Omnipresent → This is a synonym meaning "present everywhere at the same time."
Option 2: Universal → This is a synonym meaning "present or applicable everywhere."
Option 3: Common → This is a synonym meaning "occurring frequently or widespread."
Option 4: Rare → This is the antonym meaning "not found often; uncommon or scarce."
Hence, Option 4: Rare → Ubiquitous means "present everywhere," so its opposite is something that is seldom found or uncommon → correct