“I’m a student at/from/of/in the XYZ department?
If the question is:
What department are you in?
The answer could be:
- I’m a student at the Computer Science Department.
Meaning: this answers the question exactly by quoting the name of the department. The asker gets his answer and is now assured that there is indeed a Department in your college with the name “Computer Science”.
Or
- I’m a student in Computer Science.
Meaning: this tells about the stream of learning. There could be multiple departments under this stream. It’s a generic answer. The asker gets a general understanding about what your department is all about. But he doesn’t yet know what exactly the name of the department is.
or
- I’m a student in the ComputerScience department.
