sir, how many questions i should do so that i could get more than 95 percentiles . what will be the rank of my if i will belongs to obc catogary

You haven't mentioned the exam that you are enquiring for. But your profile shows that you are an Engineering aspirant. So it seems you are asking about Jee Mains. Going by last year's statistics, for 95 percentile in Jee Main you need to score around 100 to 110 Marks. As per the new exam pattern of Mains, there will be 20 objective questions in each three sections and 10 numerical problems among which you have to solve at least 5 problems. Now there is negative marking. So attempting all the questions is not recommended if you are not sure about the answer. For 95 percentile in Jee Main, you should try to attempt around 40 to 45 questions at least and only if you are sure about the answer. To help you with your Jee Main preparation, Careers360 has come up with Jee Main Knockout package https://learn.careers360.com/knockout-jee-main-april/