Final answer:
The M:N (many-to-many) relationship requires a separate table, known as a join table, in a relational database to manage the multiple associations between rows in the involved tables.
Step-by-step explanation:
The type of relationship cardinality that must be implemented in a relational database as a separate table is the M:N (many-to-many) relationship. In a 1:1 (one-to-one) relationship, each row in one table is related to one and only one row in another table, and often they can be combined into a single table. In a 1:N (one-to-many) relationship, a row in one table can be related to many rows in another table, but they can still be implemented in just two tables.
However, in an M:N relationship, multiple rows in one table can be related to multiple rows in another table, which requires a separate join table to manage these relationships. This join table typically contains foreign keys that reference the primary keys in each of the two other tables involved in the many-to-many relationship.
Examples of M:N relationships include the relationship between students and classes in a school database where each student can enroll in multiple classes, and each class can have multiple students enrolled.