Answer: (iv) Web server

The architecture of a data warehouse is built from a fixed set of components: source data, ETL (Extract, Transform, Load) tools that move and clean the data, the warehouse database itself, metadata (data about the data — schemas, definitions, mappings, lineage), an OLAP/DSS engine for analytical processing, and front-end reporting and analysis tools. A web server is not one of them: it may host an application that uses the warehouse, but it belongs to the web/application tier, not to the warehouse architecture.

Metadata, ETL tools and OLAP are all standard textbook components of a data warehouse — which is exactly why they are wrong answers in a 'NOT' question. The task is to spot the option that belongs to general web infrastructure rather than to the warehouse itself.