Negative testing is crucial in ensuring the robustness of an API, especially when dealing with diverse user input. It involves identifying potential edge cases, invalid inputs, and unexpected scenarios. By testing with a variety of inputs, you can uncover vulnerabilities and weaknesses in the API's handling of diverse data, ultimately improving its reliability.

In large-scale API testing, scalability is crucial as it ensures that the automation tool can handle a large number of test cases efficiently. Scalability enables parallel execution, which speeds up the testing process. It also helps in distributing test execution across multiple machines, ensuring optimal resource utilization. Reporting capabilities are essential for tracking and analyzing test results, providing insights into the overall test health. While script reusability is beneficial, it is not as critical as scalability for large-scale API testing.

The correct option is 404. This status code indicates that the server could not find the requested resource. It is a standard response for situations where the server cannot locate the requested URL on the server.

The advanced feature in Postman that allows dynamic and conditional scripting in tests is the Test Scripts. With Test Scripts, you can write JavaScript code to perform complex validations, manipulate data, and create conditional logic. This flexibility enhances the testing capabilities of Postman, making it a powerful tool for API testing with dynamic scenarios.

For effective API testing in a CI/CD pipeline, it is crucial to maintain an updated Staging environment. The Staging environment closely mirrors the production environment and allows teams to validate the API's behavior in a controlled setting before deploying to production. This helps ensure a smooth transition and reduces the risk of issues in the live environment.

Implementing caching is a long-term solution to reduce the frequency of API requests, thereby mitigating the impact of hitting rate limits and improving overall performance.

Negative testing involves sending invalid types of data to check how well the API handles unexpected inputs. Valid data is used in positive testing, not negative testing.

The access token in OAuth is primarily meant to identify the user who authorized the application, allowing the application to access resources on behalf of that user. It does not necessarily identify the client or resource server.

Continuous Integration (CI) primarily aims to detect defects and issues early in the development lifecycle by integrating code changes frequently. By doing this, it ensures that software quality is maintained and potential integration issues are identified at an earlier stage, making them quicker and often less costly to resolve. This speeds up software delivery and ensures a more stable and reliable codebase.

The primary goal of functional testing is to validate that each function of a software application operates in conformance with the requirement specification. For mobile apps, this ensures that all features work correctly and as intended, covering all scenarios including failures and edge cases.