Which service provides a fast, in-memory caching layer for an app that performs frequent queries?

Azure Redis Cache is the correct choice because it is a fully managed, in-memory data store based on the open-source Redis (Remote Dictionary Server) project. It provides a high-performance, low-latency caching solution ideal for frequently accessed data, significantly speeding up application responses by reducing the need to query slower backend databases. Azure Blob Storage is for storing large amounts of unstructured data, not for in-memory caching. Azure SQL Database is a relational database service, not a caching layer. Azure Data Lake is a scalable data storage and analytics service, not designed for in-memory caching for application queries.