Binary Search is the optimal approach for searching in sorted arrays due to its logarithmic time complexity O(log n). Linear Search is inefficient for large datasets, Hashing may not be suitable for sorted arrays, and Indexing might introduce additional overhead in a distributed system.

IPv6 uses 128-bit addresses, which is a significant increase from IPv4's 32-bit addresses. This expansion allows for a much larger number of possible unique addresses, addressing the issue of IPv4 address exhaustion. Therefore, "128" is the correct option.

Normalization involves breaking down data into multiple tables and using relationships like foreign keys to link them together. This ensures data is not duplicated, reduces redundancy, and allows for efficient querying and data retrieval. Storing all information in one table would lead to data redundancy and inefficiency. Using multiple databases or denormalization would not adhere to normalization principles.

Semaphores and mutexes differ in signaling and resource access. A semaphore can handle multiple resources by using a counting mechanism, allowing multiple threads to access resources concurrently. It uses signals to manage resource availability. On the other hand, a mutex is binary, meaning it only allows one thread access to a resource at a time, using a blocking mechanism to prevent other threads from accessing the resource until it's released.

Optimizing database queries in Django involves various strategies such as indexing commonly queried fields, denormalizing data to reduce joins, and using efficient ORM methods like select_related and prefetch_related to minimize database hits and improve performance.

Middleware functions in Express.js have access to the request and response objects, as well as the 'next' function which is used to pass control to the next middleware function in the stack.

The OSI Model, or Open Systems Interconnection Model, is used to provide a conceptual framework that standardizes the functions of a networking or telecommunication system into seven layers. It helps in understanding and designing complex network architectures by dividing the communication process into manageable layers, each responsible for specific tasks. Option 2 is correct because the OSI Model indeed provides a structured framework for various networking devices to communicate effectively.

Middleware in Express.js executes additional functions between receiving a request and sending a response. It can perform tasks like authentication, logging, parsing data, and modifying the request/response objects. Middleware functions have access to the request object (req), response object (res), and the next middleware function in the applications request-response cycle. This flexibility allows developers to modularize and enhance the functionality of their Express.js applications.

The "C" in ACID stands for Consistency. This property ensures that all database transactions must follow rules and constraints defined in the database schema, maintaining data validity and integrity before and after each transaction.

Heap Sort is the ideal choice for implementing a priority queue. It has a time complexity of O(n log n), making it efficient for maintaining a priority queue structure. Selection Sort, Bubble Sort, and Merge Sort have higher time complexities and are less suitable for priority queue operations.