Hello Shivani,
The question asked by you is very genuine. Look most of the exams have OMR system of answering. For this the the chances of error is very less.
However if answers of any particular questions is wrong defaultly, then you might have to wait for the answer key.
From there you can either send a letter of complaint,if you find any error or otherwise you can simply match your answer with the answer key.

i think u have to wait until the release of official answer key