MS-Windows, Linux, and Ubuntu are all operating systems, used to manage the hardware and software resources of a computer. An operating system also provides various services for computer programs.

Option 1, MS-Windows, is a graphical operating system developed by Microsoft. It includes a range of system programs that manage operations such as handling input and output and providing a user interface.

Option 2, Linux, is an open-source operating system modelled on the UNIX operating system. It`s robust and efficient, making it a popular choice for servers and other high-demand applications.

Option 3, Ubuntu, is a type of Linux distribution, which means it includes the Linux operating system along with other software.

Option 4, MS-Excel, is not an operating system. It`s an application software used for data organization, storage, and analysis. In an operating system environment, applications like MS-Excel work in conjunction with the operating system to perform tasks. Hence, the correct answer given states that MS-Excel is not an operating system.