An Intrusion Detection System (IDS) plays a crucial role in network security by monitoring network traffic for any suspicious or malicious activity. It doesn't prevent all cyberattacks but rather detects potential threats in real-time, providing alerts to administrators so they can take appropriate action to mitigate the risk. IDS helps in identifying unauthorized access attempts, anomalies in network traffic, and other security breaches, contributing significantly to overall network security posture.

React.js is primarily used for building user interfaces in web development. It allows developers to create interactive and dynamic UI components that update efficiently when data changes. React.js focuses on the frontend aspect of web development, handling the visual presentation and user interaction of web applications.

The "Content-Type" header in RESTful API requests specifies the format of the data being sent in the request body. For example, it can be "application/json" for JSON data or "application/xml" for XML data.

A router's primary purpose is to direct network traffic between different networks. It uses routing tables to determine the best path for data packets to reach their destination. This includes directing data between devices on the same network and between different networks, such as a local network and the internet. Routers also provide network address translation (NAT) to allow multiple devices on a network to share a single public IP address.

The INSERT command is used in SQL to add new records (rows) to a table. It allows you to specify the values for each column in the new row or provide values for a subset of columns if the table allows NULL values or has default values defined.

First Normal Form (1NF) requires that each attribute value within a table should be atomic or indivisible. This means that an attribute should not contain multiple values or be a composite of other attributes. Ensuring atomicity helps maintain data integrity and facilitates efficient data manipulation.

A database system ensures durability, one of the ACID properties, by using techniques like Write-Ahead Logging (WAL). In WAL, before modifying data in the database, the system first writes the changes to a log file on disk. This log file acts as a record of all transactions, and in the event of a system failure, the database can recover by replaying the logged transactions from the log file to restore the database to a consistent state. This ensures that even if the system crashes, committed transactions are not lost and the database remains durable. Other techniques such as checkpoints and transaction logs also contribute to ensuring durability in database systems, making them robust against failures.

In a priority queue, elements are dequeued based on their priority level, where higher-priority elements are dequeued before lower-priority elements. Priority queues are often implemented using heaps to efficiently maintain the highest priority element at the front.

Optimizing a slow SQL query on a large dataset involves using proper indexing techniques. Indexes help the database system locate and retrieve data more efficiently, leading to faster query execution. Rewriting the query using optimized SQL syntax can also improve performance. Increasing server RAM or adding more data won't directly optimize the query's speed.

The correct option is 'Enqueue.' In a queue, the Enqueue operation adds an element to the rear, following the FIFO (First-In-First-Out) principle where the element added first is removed first.