Consider a relational table with a single record for each registered student with the following attributes. 1. $Registration\_Num$: Unique registration number of each registered student 2. $UID$: Unique identity number, unique at the national level for each citizen 3. $BankAccount\_Num$: Unique account number at the bank. A student can have multiple accounts or joint accounts. This attribute stores the primary account number. 4. $Name$: Name of the student 5. $Hostel\_Room$: Room number of the hostel Which of the following options is **INCORRECT**?

A candidate key must uniquely identify each record (tuple) in a relation.

• (A) is INCORRECT (and hence the correct answer): Since students can hold *joint accounts*, two or more different students may share the same primary bank account number. Therefore, $BankAccount\_Num$ is not guaranteed to be unique across all student tuples and cannot serve as a candidate key.

• (B) is correct: $Registration\_Num$ is unique for each registered student, so it can be chosen as the primary key.

• (C) is correct: $UID$ is unique at the national level. If all students belong to the same country, their $UID$ values will be unique across the relation, making it a candidate key.

• (D) is correct: If $S$ is a superkey, adding any set of attributes to $S$ (such as $UID$) preserves the superkey property ($S \cup UID$ remains a superkey).