Which statement best describes ACID properties?

• A. It guarantees atomicity only.
• B. It guarantees consistency, isolation, and durability (ignores atomicity entirely).
• C. It guarantees atomicity, consistency, isolation, and durability.
• D. It guarantees immediate consistency in all distributed systems.

Answer: (C)

The concept being tested is what ACID stands for and what each property guarantees in a transaction.

ACID means atomicity, consistency, isolation, and durability. Atomicity means the transaction is all-or-nothing: either every operation succeeds and the whole change is committed, or none do and the system rolls back to its previous state. Consistency ensures that a transaction moves the database from one valid state to another, preserving all defined rules and constraints. Isolation guarantees that concurrent transactions do not interfere with each other; the effect of a transaction is as if it ran alone. Durability means once a transaction commits, its results are permanent and will survive system failures.

The other statements fall short because they omit one or more properties or misstate them. For example, focusing only on atomicity ignores the importance of preserving integrity (consistency), preventing interference (isolation), and persisting changes (durability). The idea of “immediate consistency in all distributed systems” isn’t accurate for ACID, which doesn’t guarantee such a broad distributed consistency guarantee.