In relational database management, which of the following is/are…

Answer: Both uniqueness and irreducibility.

• Uniqueness: No two distinct tuples in the relation can have the same values for the candidate key attributes. For example, a student_id that uniquely identifies each student.

• Irreducibility (minimality): No proper subset of the key's attributes can uniquely identify tuples. For example, if (course_id, student_id) together identify an enrollment, neither attribute alone identifies the enrollment, so the pair is minimal.

• Why other choices are incorrect: Uniqueness without minimality may describe a superkey that has unnecessary attributes; minimality without uniqueness cannot identify tuples. Therefore a candidate key requires both properties.