Sir, I scored 72 marks in JEE MAINS and 90% in CBSE BOARD,and I have reservation in SC .What will be my ranking? Will I get any NIT?

Hi
You can get NIT with your category reservation. DO look into the couselling and branches carefully.

Hi..
For the ranking, you can refer to the rank predictor given on the askiitians website.
http://www.askiitians.com/iit-jee/main/rank-predictor.html
Now, as per the marks you are describing, your marks are little less to get into a good NIT.
But, may be taking into account your state rank as well as your category rank, you may get a seat in an NIT. But, then you have to be very sure about the branch you will be getting, as at this marking the chances are less.
Hope you take th eright decission.
Regards.