Which of the following attributes can be considered as composite,…

Concept

Three independent properties of an entity attribute are being tested together:

• Composite: an attribute that can be split into smaller meaningful sub-parts (for example, Address into street / city / PIN).

• Single-valued: an attribute that holds exactly one value per entity (the opposite of multi-valued).

• Key: an attribute whose value is unique, so it can identify one entity unambiguously.

The answer must satisfy all three properties at the same time, so the safest method is to start from the strictest, least-common property and eliminate.

Apply the strictest test first: the key requirement

Uniqueness is the property the fewest attributes have, so test it first. Among the choices, only an enrollment number is guaranteed unique per student, so it is the only possible key. Age, date of birth and gender all repeat across different students, so none of them can be a key, and each is therefore eliminated regardless of its other properties.

Confirm the remaining properties

Each student has exactly one enrollment number, so it is single-valued. By convention institutions encode structure inside it, for example [Year]-[Stream]-[RollNo], so it can be decomposed into meaningful sub-parts and is treated as composite. It therefore satisfies all three requirements, while the eliminated options fail on the key requirement.

Why the close distractor still fails

• Date of birth is the strongest trap: it is genuinely composite (day / month / year) and single-valued, but two students can share a birth date, so it is not a key and cannot be the answer.

• Age is single-valued but atomic (not composite) and not unique; it is also usually derived from date of birth.

• Gender is a simple, single-valued attribute that is neither composite nor unique.

Result: an enrollment number is the only attribute here that is simultaneously composite, single-valued and a key.