Which of the following is not a non-functional requirement?

Explanation

Non-functional requirements describe quality attributes and constraints on how well a system performs, not what it does. Portability, security and scalability are all classic quality attributes and therefore non-functional. User interaction, however, describes the actual services and dialogues the system must offer to the user — what the system does — which makes it a functional requirement. Hence option (iv) is the one that is not non-functional.