Abhay first of all 12th class percentage is neither used by IITs or NITs for admission both of them only use JEE Advanced rank and JEE Mains rank respectively to give admission. 

I am sorry to say that with 52557 rank, forget about CS branch getting admission in one of the top NITs will not be possible for your son. Your son can only get admission in any of the NITs only if your son belongs to a state where there is a lower ranked NIT then with the help of state quota your son might get admission in any of the NIT. I am sorry to say that with this rank even getting admission in the top IIIT will not be possible but still, your son might get admission in one of the newer IIITs like IIIT Bhopal, IIIT Pune, IIIT Surat etc, which has been started 1-2 years back.

To get a better information you can still check out the following links for knowing the last 2-year cut-off of all the NITs and IIITs which will give you a fair understanding of your position:

• https://engineering.careers360.com/articles/jee-main-cutoff-for-top-iiits
• https://www.entrancecorner.com/engineering/jee-main-2017-cutoff/

You can also find out the list of private engineering colleges where your son has a high probability of getting admission by going through the following link:

• https://engineering.careers360.com/jee-main-college-predictor

And regarding JEE Advance examination although it's final result will be declared on 10th June 2018 but still tomorrow official answer key will be released and your son's optical response sheet containing all the answers marked by your son has been already released on 25th May 2018 which you can download by logging in the candidate's portal. This will help you in calculating the marks for your son which will give you a good idea about the JEE Advance result.

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