Greetings!

Sir, at 255 marks it is not going to be possible for your son to get CSE or Electronics in BITS, so your best bet is going to NITs and IIITs.

In NITs or IIITs, now considering about 10K rank and that you belong to general, category, your son should be able to get ECE in SVNIT, or NITs that rank around it.

In IIITs you can get IIIT Guwahati/Lucknow CSE, or IIITs of similar range.

Now the thing that you need to know is that in case of IIITs/NITs sometimes a lot depends on home state quota too, so if your native state has a really good NIT/IIIT then you must also try there, for example if you are a resident of Delhi, then you have really good chance of getting CSE related courses in IIIT Delhi, which is a much better than mentioned options, as I have not considered any reservations whatsoever.

To get a more knowledge on which colleges your son can get, you can use the following predictor

https://engineering.careers360.com/jee-main-college-predictor?utm_source=qna&utm_medium=jee_cp