The question word "WHICH" needs to be followed by a noun to make sense.
Not necessarily. "which" can be, and usually is, an interrogative pronoun. To turn a question with which, what or who into the reported speech, the best way to decide the order of words is to imagine what the answer will be.
If the question is:
- Which is your seat?
the answer is more likely to be:
- This is my seat.
- My seat is this.
This shows that "which" is the subject, not the subject complement, in both the direct and the embedded or indirect question, so the usual word order will be (A).