Final answer:
A firewall is a security system that prevents unauthorized access to a network's data and information. It monitors traffic and enforces security rules to create a barrier between trusted and untrusted networks. The other options refer to different security measures or technologies.
Step-by-step explanation:
A security system consisting of hardware and/or software that prevents unauthorized access to data and information on a network is called a firewall. This system monitors and controls incoming and outgoing network traffic based on predetermined security rules. Essentially, a firewall serves as a barrier between a trusted internal network and untrusted external networks, such as the internet.
An encryption system refers to the process of converting information or data into a code, especially to prevent unauthorized access, but does not directly prevent access to the network itself. An intrusion detection system (IDS) is a device or software application that monitors a network for malicious activity or policy violations, but again, is not itself a barrier. An authentication barrier would involve verifying identities before granting access, but it does not necessarily prevent unauthorized network traffic. Therefore, the correct answer to the student's question is option a. Firewall.