Final answer:
The normal form in which all key attributes are defined, ensuring non-key attributes are dependent only on the key, is Third Normal Form (3NF).option a.
Step-by-step explanation:
The normal form where all key attributes are defined, and, in addition, any non-key attributes are dependent on the key, and only the key, is the Third Normal Form (3NF). To reach 3NF, a table must first satisfy the criteria for the First Normal Form (1NF) and Second Normal Form (2NF). In 1NF, the table must have atomic values with no repeating groups or arrays. When a table is in 2NF, it means that it is already in 1NF and all the non-key attributes are fully functionally dependent on the primary key. A table is in 3NF if it is in 2NF and all the non-key attributes are not only fully functionally dependent on the primary key but are also non-transitively dependent (i.e., no non-key attribute depends on another non-key attribute).
The correct answer is 1NF (First Normal Form). In 1NF, all of the key attributes are defined and there are no repeating groups or arrays of values within a single record. Each attribute contains a single value and there are no composite attributes. An example of a 1NF table would be a simple table of students and their grades, where each student has a unique ID and a single grade.