Hello Harshal,
In my mind I have answered this question more then once, however no answers in this forum.
Your biggest problem with alphanumeric ID's is the amount of possible symbols. The software does not discriminate between numbers and characters.
In your example, it is possible to make an layout with 5 possible answers AB 012, and forget the space in between. Or you make 2 groups of questions, one with the characters for the first 2 symbols and then without the digits.
Make sure the order in wich you receive the symbols is correct.