Which statement best contrasts relational databases with NoSQL databases?

• A. Relational DBs use structured schemas and SQL; NoSQL supports flexible schemas and non-relational models.
• B. NoSQL uses SQL and fixed schemas; Relational uses dynamic schemas.
• C. Both rely on ACID in all cases.
• D. NoSQL cannot scale horizontally.

Answer: (A)

Schemas and data models are the main distinction here. Relational databases organize data into tables with a fixed, predefined schema and use SQL to query and manage that data, with strong emphasis on structured relationships via foreign keys. NoSQL databases, on the other hand, often use schema-flexible or schema-less designs and employ non-relational models such as documents, key-value pairs, wide-column stores, or graphs, with query capabilities that are not strictly SQL.

That contrast is why the correct statement marks relational systems as structured with SQL, and NoSQL as flexible in schema with non-relational models.

The other ideas fail because NoSQL can still use non-SQL approaches and is designed to scale horizontally, rather than being limited to fixed schemas or vertical scaling, and not all systems maintain ACID in every case.