Oh, I've just noticed your comment. So we can agree that it is just the old style of teaching when they supposed that not knowing a language = being a bit stupid.

The question with the definite article is very similar to the English equivalent (a bit weird except if we are talking about a particular chair that was mentioned earlier):
Ez szék? = Is this a chair?
Ez a szék? = Is this the chair? (...e.g. you mentioned earlier/we were talking about earlier...)
Although, just to puzzle you a bit further, in this latter case, you could also ask: Ez az a szék? (It is a more explicit form to refer back to our earlier discussion about a particular chair.)