Which is valid extension that user creates on operating system?

In operating systems like MS-DOS and Windows, file extensions are used to identify the type of files and associate them with specific applications or actions. Here’s a breakdown of the options:

Exe: This extension typically denotes executable files in Windows. Executable files contain instructions that a computer can execute directly.
Com: This extension is used for command files in MS-DOS and Windows. It stands for "command".
Sys: This extension is used for system files in MS-DOS and Windows. System files are essential files used by the operating system.
Bat: This extension is used for batch files in MS-DOS and Windows. Batch files contain a sequence of commands that are executed one after another.

Therefore, the correct answer is Option D: Bat.