With a Percentile of 96.8 in JEE Main, he has great chances in securing a seat in some of the Good NITs, IIITs as well as Top GFTIs like PEC, IIEST or BIT Mesra. However, I would suggest him to improve over the next 3 attempts of JEE Main and target anywhere near 99 Percentile for better prospects during Counselling.

Being Interested in Physics, I would suggest him to choose between Electronics/Electrical or Mechanical Engineering. Both of the branches have great career scope and placement prospects today in India, in both the private and public sector. If not Mechanical, he may select between Aerospace or Metallurgical Engineering, both of which have a fair share of Calculus, Physics, Optics and Mechanics. Perhaps if he has a knack in Computer Applications and Mathematics he should prefer CSE or IT Branch respectively.

For more information and College Prediction do follow the link below

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

With a Percentile of 96.8, your son's estimated rank will be anywhere around 35k. Assuming he is from General Category, you will have the following best options subject to his interest in Physics

1. Metallurgical Engineering

MNIT Jaipur, MANIT Bhopal, NIT Jamshedpur, VNIT Nagpur

2. Mechanical/Electrical/EC

NIT Andhra Pradesh, NIT Agartala, NIT Manipur, NIT Sikkim, NIT Srinagar, NIT Nagaland

3. Electrical/EC

IIIT Bhopal, IIIT Bhubaneshwar

For more information and Rank Prediction do follow the link below