Final answer:
A table is considered a relation when it has entity integrity, meaning each row is unique and identifiable by its primary key.
Step-by-step explanation:
Entity integrity is concerned with ensuring that each row of a table has a unique and non-null primary key value; this is the same as saying that each row in a table represents a single instance of the entity type modelled by the table. Entity integrity relies on the creation of primary keys — the unique values that identify pieces of data — to ensure that data isn't listed more than once and that no field in a table is null. It's a feature of relational systems which store data in tables that can be linked and used in a variety of ways.
For a table to be considered a relation, which is a concept often used in databases, it must follow certain integrity rules. The correct answer from the provided options is a. Entity integrity, which ensures that each row in a database table is unique and identifiable by its primary key. Unlike referential integrity that refers to maintaining the consistency of links among data in different tables, entity integrity deals more with the uniqueness of data within a single table. Additionally, the physical domain and logical domain are not directly related to a table being a relation.