When a boy and girl meets for the first time with the intention of doing discussion with each other and make marriage with each other, then in the very first meeting, is it allowed for the girl to remove her hijab and be without 100percent hijab in front of the boy, so that the boy knows her more, and is it allowed for the boy to see her in the very first meeting? if not, then at which stage is it allowed?

If the boy is serious about the marriage, and the probability of choosing this girl as a wife is high, then yes.