Me and a friend of mine had won similar quiz competition called Quest 2000 (jointly organized by Nehru Science Center and KC College) in Dec. 2000. The pattern of the quiz was as follows
1. First round - written (which you have already cleared)
2. Verbal round - This consisted of 4 rounds
(Round A) Choose your fav topic - we had the options of Space Sciences, Chemical Technology, Biotechnology, Physics, Computers & Internet
(Round B) Identify the experiment/ law - An experiment was performed live and we had to identify the purpose of the experiment and give a brief description (the experiment is generally from the syllabus, so if you have been studying well at school/ college you will clear this)
(Round C) General round - this round has typical quiz questions related to scientust, inventors and their discoveries, theories, inventions, etc.
(Round D) Rapid fire - simple questions are asked for 2/3 minutes and you have to answer each question withing 2 seconds, the more questions you answer within you time frame, the more you score. This round may have negative markings so in case you do not know, don't answer but DON'T GIVE INCORRECT ANSWERS. Questions are simple but tricky (we were asked what is the colour of bat's egg? Bat is a mammal and lays no egg but under the pressure we said PASS)
Reference - Most importantly you should be well versed with your syllabus. Refer to any good Science quiz books (Science Quiz Book by Rajeev Garg, Pustak Mahal Publ.; Mathematics Quiz Book, also by Pustak Mahal Publ) plus some good web sites for astronomy, defence (www.bharat-rakshak.com)
If you do love reading books beyond your syllabus you will easily clear all rounds. ALL THE BEST!!!