If the rank is known then you can have the idea that whether your son will be getting the seat or not. Here you have also not mentioned the branch in which your son wants to get enter because the possibility of admission can only be known by the cutoff marks of the particular branch. Different branches have their own closing ranks based on the entrance taken by the respective department. And your son has to go for the counselling process then only one must ensure the possibility of admission. Still I am providing you the site where you can find out the closing ranks through BITSAT in various branches, you will have some idea about the cutoffs.

www.careers360.com/colleges/banglore-institute-of-technology-banglore/cut-off