Transitioning from a SOAP API to a RESTful API may require changes in the Protocol used to send requests and receive responses. SOAP and REST use different communication protocols and data formats.

Postman is a popular tool used for testing APIs. It provides a user-friendly interface for making API requests, inspecting responses, and automating tests. Developers use Postman to ensure that their APIs work correctly and as intended.

Managing test data dependencies in an end-to-end API test is best achieved by using a centralized test data management system. This approach ensures that test data is organized, versioned, and easily accessible to the testing framework, allowing for consistent and reliable data usage during API testing.

JSON Web Tokens (JWT) assist in authorization processes by providing a secure way to transmit claims between parties. These claims can include information about the user, permissions, and more. JWTs are digitally signed, ensuring data integrity, and they can be used for stateless authentication, which is essential for web applications.

In this scenario, the most appropriate approach is option B. To ensure that an API can handle a large volume of requests, you should use load testing tools to simulate high request volumes and analyze its performance under load. Option A, with a small number of requests, may not reveal potential issues, and option C is not a reliable method for load testing. Option D neglects the importance of load testing.

Using GraphQL, clients can specify their data requirements in a "Query Document." This document outlines what data the client needs, allowing for precise data retrieval. This approach contrasts with REST, where clients often receive more data than necessary.

In GraphQL, the blank is filled by "Query Language." GraphQL allows clients to define precisely the data they require, eliminating over-fetching or under-fetching, and this is achieved through a query language designed specifically for this purpose.

When deciding between REST, SOAP, or GraphQL for a new API, crucial considerations include data serialization format, platform compatibility, and the need for strict versioning. These factors can significantly impact how data is transmitted, processed, and maintained in the API.

Developers might need to create custom HTTP methods for their Web APIs in scenarios where the standard HTTP methods (GET, POST, PUT, DELETE, etc.) lack the expressiveness or functionality required for their specific use case. Creating custom methods is allowed within the HTTP standard, but it should be done judiciously and documented well to ensure clarity. They are typically used when there is a genuine need for additional, non-standard functionality that cannot be achieved using the standard methods.

When changes to an API are not backward compatible, versioning can help in preventing disruptions to existing clients. API versioning allows the introduction of new features and changes without affecting existing clients, making it easier to manage changes while maintaining compatibility with older versions.