Which one among the following is the purpose of firewall?

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Its primary purpose is to establish a barrier between a trusted internal network and untrusted external networks (like the internet), thereby preventing unauthorised access to the computer system. It is not a virus scanner (which is the job of antivirus software), nor does it install software or record user activity. Hence, option (a) is the correct answer.