Developers may choose to create a Web API instead of a traditional web application to enable integration with other systems. Web APIs allow different software applications to communicate and interact, making them ideal for data exchange and third-party integrations. Providing a graphical user interface, offering a mobile app, or improving website performance may be goals but are not primary reasons for creating a Web API.

When implementing API key rotation, it's crucial to consider security best practices. API keys should be changed periodically to reduce the risk of unauthorized access. Sharing keys with everyone or storing them in public places should be avoided. Storing keys securely, managing access, and ensuring that compromised keys can be revoked are important aspects of API key rotation.

GraphQL allows for more flexibility in querying data compared to REST because it enables clients to specify the structure and fields of the response, allowing them to request only the data they require. In contrast, REST often returns fixed data structures, and clients must make multiple requests to retrieve the needed data.

Load testing an API involves assessing its performance under a specific load. This test measures how well the API can handle a high volume of concurrent requests or transactions, helping identify performance bottlenecks and ensuring the API's reliability under heavy usage.

Optimizing the performance of APIs is essential for ensuring responsiveness. Minimizing database queries and employing caching mechanisms can significantly reduce response times. Caching allows you to store frequently accessed data in memory, reducing the need for repeated database queries. This is a recommended practice for performance optimization.

Automated testing for APIs can present challenges in terms of limited scalability, as maintaining test automation can become complex as the number of APIs grows. It is essential to ensure that the test automation framework can handle the increasing number of API endpoints and scenarios.

The purpose of debugging in API development is to identify and fix issues or errors in the API code and functionality. Debugging helps ensure that the API works as intended, and it is a critical step in the development process to deliver a reliable and error-free API to users. Debugging does not aim to introduce errors, enhance security, or slow down the API.

API security concerns include protecting against unauthorized access, SQL injection, and data breaches. SQL injection is a type of attack where an attacker injects malicious SQL code into input fields, potentially compromising the database and exposing sensitive information.

Monitoring a critical API requires tracking relevant metrics. Prioritizing error rates and system resource utilization (Option 3) is the most appropriate choice, as it helps identify issues and performance problems. Response times are essential but should not be the sole focus. Option 1 suggests ignoring anomalies, which is not advisable, and option 2 is less relevant to anomaly response. Option 4 lacks the essential focus on error rates and resource utilization.

The correct approach to securely store and use an API key is to utilize environment variables or a secure key management system. Storing API keys in plain text or in version-controlled files is insecure and should be avoided. Encrypting and storing in a restricted database could be an option but may not be as secure as using dedicated key management solutions.