Dear aspirant,

Ever since last year the pattern for JEE mains has changed into percentile system from mark system. So, you can't exactly say what marks you should score at minimum to be eligible for JEE advance.

But if you score somewhat around 90 percentile being an OC candidate you'll be able to give JEE advance. For getting around 90 percentile ; out of 300 you must target to score around 110+ . Only than you can be sure to get the chance of giving JEE advance. Maybe even 100 marks will secure your place in JEE advance even. But just to be sure target 110+.

Hope this helps and all the best!