Which of the following is not a Non functional requirement?

Final answer: User interaction is not a non-functional requirement; it is a functional requirement.

What are non-functional requirements? They describe system qualities, constraints, or performance characteristics (how the system should be). Examples include:

• Portability: how easily the software can run in different environments or platforms.

• Security: protection requirements such as confidentiality, integrity, and availability.

• Scalability: the system's ability to handle growth in users or load.

Why user interaction is not a non-functional requirement: User interaction specifies concrete behaviors and features the system must provide to users (for example, user interfaces, workflows, and inputs/outputs). These describe what the system does, so they are functional requirements.

Therefore, the correct choice is the option labeled "User interaction" because it is a functional requirement, while portability, security, and scalability are non-functional requirements (quality attributes).