Which of the following file types is NOT supported by the Serverless SQL Pool in Azure Synapse Analytics?

The Serverless SQL Pool supports Parquet, CSV, JSON, and Delta Lake formats for querying files in Azure Data Lake or Blob Storage via OPENROWSET. Avro format is not in the supported file format list for Serverless SQL Pool, making it the correct answer for the unsupported format.

Parquet is one of the primary and most performant formats supported by Serverless SQL Pool's OPENROWSET function.

JSON files are supported by Serverless SQL Pool and can be queried using OPENROWSET with the appropriate WITH clause or JSON_VALUE functions.

CSV (and other delimited text formats) is fully supported by Serverless SQL Pool and is one of the most commonly queried file types.