Which of the following describes the primary purpose of a transaction in a database?

The primary purpose of a transaction in a database is to ensure database integrity. Transactions are a series of operations executed as a single logical unit. They follow the ACID properties—Atomicity, Consistency, Isolation, and Durability—which are essential for maintaining the accuracy and reliability of data in a database.

When a transaction is completed successfully, it should leave the database in a consistent state. If any part of the transaction fails, the entire transaction is rolled back, preventing partial updates that could lead to data inconsistency. Thus, transactions are crucial for protecting the integrity of the database, ensuring that all the data remains accurate and reliable throughout various operations. This integrity is foundational to the overall functioning of relational databases, making option B the correct choice.