An operating system that helps in sharing files across a network is known as…

Operating systems are classified by the specific management role they are built to perform. A Network Operating System (NOS) is the category whose defining role is managing network resources: it supplies the protocols, security, and coordination logic that let multiple independent computers on a network communicate with one another and share files, applications, printers, and other hardware devices.

The question asks for the operating system that "helps in sharing files across a network" — that description matches the core function of a Network Operating System, which runs on servers and workstations in a LAN/WAN to manage shared access to files and devices for many connected users.

• Real Operating System is not a standard OS category; the related real term is a Real-Time Operating System (RTOS), which is built around meeting strict timing deadlines for embedded/control tasks — not around network file sharing.

• Time-Sharing Operating System lets many users share the processing time of a single machine by rapid context-switching — a different concern from connecting multiple machines so they can exchange files over a network.

• Coupling describes how tightly or loosely a system's own components are connected to each other (e.g., tightly coupled vs. loosely coupled systems) — it is not a category of operating system at all.

Since only the network-resource-management role matches the description given in the question, the operating system being described is the Network Operating System.