Which of the following is not a Non functional requirement? 

The correct answer is User interaction

Key Points

• User Interaction:  This is generally considered as part of the functional requirements rather than the non-functional requirements. User interaction refers to how a user will interact with the system—what functions they can perform, what outputs they yearn, how the system responses to their inputs, etc. These are tied to the tasks the system needs to perform and are usually described in use cases. User interaction can affect aspects like interface design, error handling, and overall system workflow.
• Non-functional requirements refer to the quality attributes or standards that the system must function within, such as security, scalability, or portability.
• Portability: This is a non-functional requirement that refers to the ability of software to be moved from one environment to another. For example, from one operating system to another (like Windows to Linux), or from one hardware configuration to another. The software, if designed to be portable, should require minimal adaptation to smoothly function in the new environment.
• Security: Security is another non-functional requirement and is essential for any software system. It refers to the software's ability to prevent unauthorized access, resist attacks, protect data, and recover from compromises. This encompasses aspects such as authentication, encryption, access controls, and audit trails.
• Scalability: Scalability is also a non-functional requirement. A scalable system is capable of handling an increasing amount of work by adding resources to the system. This means if the number of users increases unexpectedly, the system should be able to accommodate this increase without impacting performance or functionality. There are two main types of scalability: vertical (adding more power to existing hardware) and horizontal (adding more hardware to distribute the work).

So, the correct answer is User interaction