Hi,can anyone help me knowing about how many questions per block has to be correct to get score of 99.....

hey no one can give you a correct answer for that.....it depends on the time and with whom you take the exam. if you unfortunately are in a time slot with people who are really top ranker or the most intelligent guys then it will be tough to get the 99 percentile. 99 can range anywhere starting from 225 correct questions.
i know of people who got 99percentile for 228....and people who got 99percentile for 267.
so it is luck and god's blessings.