Answer:
Unique.
Explanation:
Unique is supported by a primary key because of primary key we can uniquely identify the tuple so the attribute which has been set as primary key must contain values that are unique and these values cannot be null.These values should not be changeable over time and updateable because there is a chance if these values are manipulated a copy of it may be present in that attribute.So the primary key won't be able to uniquely identify the tuple.
