What is the primary function of a firewall in network security?

The primary function of a firewall in network security is to block unauthorized access to or from a network. Firewalls serve as a barrier between trusted internal networks and untrusted external networks, like the internet, effectively controlling the flow of incoming and outgoing traffic based on predetermined security rules. This ensures that only legitimate traffic is allowed while malicious activity, such as hacking attempts or unauthorized data access, is thwarted.

While increasing wireless access, monitoring social media activities, and managing bandwidth usage are relevant tasks in network management, they do not encapsulate the core purpose of a firewall. The essence of a firewall's role lies in its ability to enforce security policies, protect sensitive data, and maintain the integrity of a network by preventing unauthorized access. This makes option B the most accurate representation of a firewall’s primary function.