Akhil with 149 marks in JEE Advanced exam under OBC category you can expect a rank around 2000 in your OBC category. Although rank can vary either side drastically because the rank is totally relative and depends on many parameters like your son's performance, other student's performance, the difficulty of the exam, number of students attended the exam etc. 

So, for final result you will need to wait till 10th June then only you will be able to figure out in which IIT, which stream you have a high probability to get admission.

Feel free to ask if you have any more queries. All the best!!