Which of the following normal forms is specifically defined to ensure that a…

Concept

Normal forms form a strict hierarchy of increasingly narrow constraints: every 5NF relation is also in 4NF, every 4NF relation is also in BCNF/3NF, and so on. Each level targets one specific class of redundancy. Fourth Normal Form (4NF) is the level that specifically eliminates PROBLEMATIC non-trivial multivalued dependencies (MVDs) — those whose determinant is NOT a superkey; an MVD X ↠ Y whose determinant X already is a superkey remains permitted. Its purpose is to stop a single relation from bundling two or more independent multi-valued facts about one entity together via such a problematic MVD.

Application

The question asks which form guarantees that a relation holds information about only a single entity. This is exactly the guarantee 4NF's own definition provides: by forcing every MVD's determinant to be a superkey, 4NF ensures a relation cannot mix independent multi-valued attributes of one entity (for example, a person's set of hobbies and their set of skills) into one table. So the form being described is 4NF.

Cross-check: why the other options don't fit

• 3NF — its own definition requires that for every non-trivial functional dependency X → A, either X is a superkey or A is a prime (candidate-key) attribute. It never examines multivalued dependencies at all, so a 3NF relation can still legally combine independent multi-valued facts about one entity.

• 5NF — its own definition requires that every non-trivial join dependency holding in a relation be implied by its candidate keys. The normal-form hierarchy makes every 5NF relation automatically satisfy 4NF as a consequence, but the single-entity/no-independent-MVD property is not what 5NF's own definition introduces or is about — that property is introduced at 4NF.

• "More than one of 3NF, 4NF, and 5NF" — this would be correct only if the stated property were the defining criterion of two or more of these three forms simultaneously. It is the specific, distinguishing definition of exactly one of them (4NF); 5NF inheriting the property as a downstream consequence of the hierarchy is not the same as 5NF's own definition being about that property.

• "None of 3NF, 4NF, and 5NF" — this is ruled out because one of these three forms (4NF) does define exactly this property.

Answer: 4NF. This matches the official answer key published for this item (BPSC TRE 3.0, Computer Science paper).