The image show that I can add more than one Department for the mentioned field
My question is, am I able to restrict that field so that it only able to select one department and no more than that? If so how? Any answer would be appreciated, thank you very much
This is definitely possible.
There is an article related to restricting the selection field along with the example code.
I posted the link below so please check it.
Though the article is about restricting the USER SELECTION field,
you will probably just need to alter few stuff for the DEPARTMENT field.