Relation Database
A relational database is a type of database that stores and organizes data into tables containing rows and columns. It is based on the relational model, which represents relationships between tables using keys. One of the fundamental components of a relational database is a tuple.

Tuple
A tuple, in the context of a relational database, refers to a single row or record within a table. It represents a complete set of data, with each field or attribute containing a specific piece of information. Tuples are used to store and represent individual instances or entities within a table.

Fields
A field, also known as an attribute, is a single piece of data within a tuple. It represents a specific characteristic or property of the entity being described. For example, in a table representing employees, fields might include attributes such as employee ID, name, age, and salary.

Domains
A domain refers to the set of possible values that a field can take within a database. It defines the data type and constraints for a particular attribute. For instance, a domain for the "age" field might specify that it can only contain integer values between 18 and 65.

Dividing Tuples into Fields
When we say that tuples are divided into fields, it means that each tuple is broken down into its individual attributes or fields. This process involves identifying and extracting the specific data values associated with each attribute within the tuple.

Significance of Domains
Domains play a crucial role in ensuring data integrity and consistency within a relational database. By defining the allowable data types and constraints for each field, domains help enforce data validation rules and prevent the storage of incorrect or invalid data. They provide a way to standardize and control the values that can be stored in a particular field.

Correct Answer
In the given question, the correct answer is option 'B' - Domains. Tuples in a relation database are divided into fields, and these fields are defined by their respective domains. Therefore, the domains represent the set of possible values and constraints for each field within a tuple.