Mutation testing involves deliberately introducing small changes (mutations) to the source code and then running the test suite to check if the tests detect these mutations. This technique helps evaluate the effectiveness of the test cases by measuring their ability to detect changes in the code, thereby improving the quality and reliability of the test suite. It is significant as it helps in identifying weak spots in the test suite and improving overall test coverage.

A VLAN Router (also called a Layer 3 switch or router) is used to facilitate communication between different VLANs. It operates at Layer 3 of the OSI model, routing traffic between VLANs based on IP addresses. This enables segregation of network traffic for security or organizational purposes while allowing controlled communication between VLANs as needed.

Encapsulation is the process of bundling data (attributes) and functions (methods) that operate on the data into a single unit called a class. It helps in hiding the internal state of an object and only exposing the necessary functionality to the outside world. This enhances security, modularity, and reusability in object-oriented programming.

The correct option is "Atomic." In the context of ACID properties, atomicity ensures that database transactions are either fully completed or not executed at all. This means that if a transaction fails or encounters an error, it will be rolled back to its initial state, maintaining data consistency. Atomicity is crucial for reliability and data integrity in database management systems.

File system fragmentation occurs when files are broken into pieces scattered across the disk, leading to increased read/write times as the system needs to access multiple fragments. This impacts performance as it introduces delays in retrieving and storing data.

When resolving conflicts in Git, the first step is to identify the conflicting files. git status helps in listing the conflicting files. Once identified, use git diff to view the differences and manually resolve the conflicts in the file. After resolving the conflicts, stage the changes with git add and then commit the resolved changes. Alternatively, you can also use tools like git mergetool to help with resolving conflicts more efficiently.

Option 1 is correct. In a social media platform, it's efficient to have separate tables for users, profiles, and relationships. This allows for easier management and scalability. Foreign keys ensure data integrity and help in querying related information efficiently. Using a single table for users can lead to data redundancy and maintenance issues. A hierarchical structure may become complex and harder to manage as the platform scales. Denormalization, while useful in certain cases, may not be ideal for handling user profiles and relationships in a social media context.

Abstraction in OOP refers to the concept of hiding complex implementation details and showing only essential features of an object. Encapsulation, on the other hand, involves bundling the data (attributes) and methods (functions) that operate on the data into a single unit, i.e., a class. This helps in achieving data hiding and access control.

Pre-order traversal is used to visit all nodes of a binary tree in a specific order. In this traversal, the nodes are visited in the order of root, left subtree, and then right subtree, making it useful for certain operations like copying a tree.

Option 4 outlines the correct approach to troubleshoot network connectivity issues between two endpoints by utilizing network diagnostic tools such as ping, traceroute, and packet capture. These tools help in identifying connectivity problems, latency issues, and packet loss, providing valuable insights for troubleshooting. Checking physical connections (Option 1) is essential but may not pinpoint specific connectivity issues. Verifying VLAN configurations (Option 2) and switch port configurations (Option 3) are relevant but are not direct troubleshooting methods like using diagnostic tools.

A Priority Queue is the most efficient data structure for managing tasks with varying levels of urgency in a concurrent execution system. It ensures that tasks are executed based on their priority levels, allowing higher priority tasks to be processed before lower priority ones. This is crucial for maintaining system responsiveness and meeting urgent task requirements promptly. Binary Search Trees, Hash Tables, and Doubly Linked Lists are not specifically designed for priority-based task management and may not offer the same level of efficiency and responsiveness as a Priority Queue.

To improve security in Node.js applications, developers should use Helmet, a middleware package that helps in securing Express apps by setting various HTTP headers to prevent common vulnerabilities like XSS attacks.