Which of the following is a supported API for JSON in Salesforce?

The Bulk API is the correct answer as it specifically supports JSON format for data interchange. This API is designed to handle large volumes of records, making it particularly useful for bulk data operations such as inserts, updates, and deletes. It operates on a more efficient model by allowing users to perform operations asynchronously, which means that the client can continue working while the server processes the request.

The Bulk API provides a streamlined way to send and receive data in JSON, which is generally more lightweight and easier to work with compared to XML, especially for web applications and services that are built around modern JavaScript frameworks. This advantage makes it a popular choice for developers who require efficient data handling capabilities.

While the other APIs listed may support XML and provide other forms of functionality, they are not primarily geared towards JSON handling in the same way that the Bulk API is. The SOAP API, for instance, typically communicates in XML, and while the Query API has functionalities for querying records, it does not specifically denote support for JSON. Thus, the Bulk API stands out as the most suitable choice for JSON support in Salesforce.