Electrical Engineering

No, three years' Diploma holders are not eligible to take admission in NIT. Apart from IIT and NIT, most colleges in India offers lateral entry for Diploma students.

Please visit this site
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/university/srm-institute-of-science-and-technology-srm-ist-Chennai-24749/reviews&ved=2ahUKEwi38ZWiqcDhAhUV63MBHYAcDwUQFjAKegQIARAB&usg=AOvVaw0vhvI_-uAKD5iBUnMk6wQZ.

Hello Naveen,
You indeed have obtained quite good marks in your diploma examination. Scoring 75% is quite good performance. I am sure with this percentage of marks you will get admission in your desired Institute and desired branch. A word of caution. Admission is a quiet dynamic process and many a times it depends on how those placed above you give their choice and in general how were the papers and how the students have scored in the exam.

For all the details visit this link: https://www.shiksha.com/engineering/course/polytechnic-engineering-diploma-wisdom-school-of-management-pune-hadapsar-213179

B.Sc is your only option, if you don't wish to pursue B.Tech.

CSE is the best branch with high scope now. But, it all depends on your interests, opt for the one you are interested in.

Hello,
There are a lot of colleges to choose from. You can refer the below link designed by Shiksha, in which college ranking, their ranking, facilities all criteria are shown, follow the link:
https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-india/44-2-0-0-0.

You can prepare for these branches in two ways:
1st you can join any institute like made easy or Ace. They are the good ones and they make the concepts clear. If you don't want to spend money in offline coaching then
2nd choice if you have ample amount of time you can always go for NPTEL and self Study. EC and EE are the most difficult branches from my 4 year of experience I am saying that. Always try to learn and practice previous year papers. Which will be very helpful.
I hope it helps.