Common errors or good writing?

I've seen some 'mistakes' written so many times around the internet, I was wondering if they were really mistakes or if I was wrong. Would things like these be appropriate for formal use?

What University do you go to?

The correct way to write that would be, "Which University do you attend?", right? I've seen "what" used in the place of "which" so many times, I was wondering if that is actually considered correct.



Is that sarcastic?

I assumed that "ic" should be replaced by "ism", is this correct?

Which is correct:

He is the Head of the Department or he is Head of the Department.

He will do it only when he receives formal authorization from you or he will do it only when he receives a formal authorization from you.