In Go, custom JSON marshaling and unmarshaling logic can be handled by implementing the MarshalJSON and UnmarshalJSON methods for custom types. This allows developers to define how their types are encoded and decoded to and from JSON. By implementing these methods, you gain fine-grained control over the JSON representation of your types, enabling you to handle complex or non-standard JSON structures. This approach is preferred over using reflection or third-party libraries as it provides better performance and flexibility.

The correct option is "pkg". In Go, the pkg directory is used to store compiled package objects that can be reused across multiple projects. When you create a package, its compiled form is placed in the pkg directory, making it accessible to other projects when imported. This promotes code reusability and modularity in Go programming.

Route middleware in Gorilla Mux is primarily used for performing operations before and after the route is handled, such as authentication, logging, or modifying the request or response.

In Go, a pointer stores the memory address of a variable. When you declare a pointer variable in Go, it holds the memory address of the variable it points to, allowing indirect access to the variable's value.

In Go, value receivers make a copy of the value when calling the method, ensuring that the original value remains unchanged. On the other hand, pointer receivers work directly on the original value, allowing modifications to the original data. This difference in behavior is crucial when deciding whether to use value or pointer receivers for methods.

Constants in Go are immutable, which means once their values are assigned, they cannot be altered or mutated throughout the program. This ensures predictability and reliability.

The correct option is "To handle HTTP requests and map them to handlers". Routing in web development with Go involves directing incoming HTTP requests to the appropriate handlers or controllers based on the request URL.

In Go, mocking frameworks like "testify" or "gomock" provide utilities for creating mock objects. Mock objects are used to simulate the behavior of real objects in controlled ways during testing, allowing developers to isolate the code under test and verify its behavior.

Optimizing database indexes can significantly improve the performance of database operations, especially for frequently queried columns. Proper indexing reduces the time taken for data retrieval by enabling the database engine to locate records efficiently. It's an essential strategy for improving overall application performance.

The switch statement in Go is used to execute one of many blocks of code based on the value of an expression. It provides a clean and efficient way to handle multiple cases without excessive nesting.

The 'new' keyword in Go is used to allocate memory for a new variable. It initializes the variable with the zero value of its type and returns a pointer to the newly allocated memory. This is particularly useful when working with composite types like structs where the 'make' keyword isn't applicable.

html/template is a built-in package in Go, specifically designed for generating HTML content. It provides strong security features like auto-escaping to prevent XSS attacks. Additionally, it offers better performance compared to text/template due to optimizations made for HTML. Ace and Mustache are also templating engines, but they lack the security features and performance optimizations provided by html/template.