Introduction:
MS-EXCEL is a widely used spreadsheet program developed by Microsoft. It is part of the Microsoft Office suite and is available for both Windows and Mac operating systems. In this question, we are asked about the operating system on which MS-EXCEL is based.

Explanation:
MS-EXCEL is based on the Windows operating system.

Windows:
- MS-EXCEL was specifically developed for the Windows operating system, which is a graphical operating system developed by Microsoft.
- Windows provides a user-friendly interface with a graphical user interface (GUI) that allows users to interact with their computer using icons, buttons, and windows.
- MS-EXCEL takes advantage of the features provided by the Windows operating system, such as the ability to resize and move windows, use menus and toolbars, and interact with other applications.

DOS:
- DOS (Disk Operating System) was an earlier operating system developed by Microsoft, which was primarily a command-line interface.
- MS-EXCEL was not based on DOS, as it was developed for Windows, which was introduced later to provide a more user-friendly interface.

UNIX:
- UNIX is a popular operating system used primarily in servers and workstations. It is known for its stability, security, and powerful command-line interface.
- MS-EXCEL is not based on UNIX, as it was developed for the Windows operating system.

OS/2:
- OS/2 is an operating system developed by IBM and Microsoft. It was designed to be a successor to DOS, providing a more advanced and modern operating system.
- While MS-EXCEL was compatible with OS/2, it was not based on it. MS-EXCEL was primarily developed for the Windows operating system.

Conclusion:
In conclusion, MS-EXCEL is based on the Windows operating system. Windows provides a user-friendly graphical interface that MS-EXCEL utilizes to provide users with a powerful and intuitive spreadsheet program.