Final answer:
The popular Network Operating System (NOS) found on web servers from the given options is 'Red Hat', specifically Red Hat Enterprise Linux. Apache is a web server software, not an operating system, and the other options are less relevant to the question.
Step-by-step explanation:
The question you've asked is regarding a popular Network Operating System (NOS) used on web servers. Among the options provided, the term 'Apache' refers to the Apache HTTP Server, which is a highly popular web server software but is not itself an operating system. The correct term for what might be considered a NOS for web servers amongst the choices would be 'Red Hat', specifically Red Hat Enterprise Linux, which is a widely used server operating system. Neither Windows 10 nor Novell Linux (the latter of which might be a confusion with Novell's SuSE Linux, but it's not typically a term used to describe a Linux distribution) is as frequently associated with the term NOS for web servers. Red Hat Enterprise Linux provides robust support and is preferred by many businesses for its stability and security features.