Hello,
You can get NIT/IIT very easily unlike General Category candidates as seats are reserved for PwD candidates. I would suggest you to prepare well to compete with other candidates as in college placements or exams there is no reservation otherwise you will suffer a lot in your college. To get lower NITs core branches like mechanical,civil you need to score in between 140 to 160. And fir the branches like CSE you need atleast 160-180. For average NITs core branches you need to score in between 200-220 and for top branches you need in between 220-230/240. For top NITs you need to score >240. IITs have a limited number of seats only i.e. 16,053 for about 2.5 lakh applicants. Given below are the number of seats as per JoSAA Seat Matrix 2021 for all the categories.
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Total Open & Reserved Seats in IITs Seat Matrix at 23 IITs.
Category                   Number of IIT Seats
ST-PwD                         58
OBC                              4126
OBC-PwD                      203
Total Seats                   16053

JEE Mains Cut off Marks for NIT 2022
Category  JEE Main Cutoff 2021            JEE Main Cutoff 2019
OBC - NCL                68                                   74.3
SC                            46.9                                  54
ST                            34.7                                  44.3
PwD                    0.0096375                         0.1137173