How difficult is it for a B.Tech CSE student to make a social media app during college days?

First of all you should have your hands clear on basic programming languages like - c, c++, python, java.
If you want to built a mobile app then you have 2 options -

You have to make only mobile app.
You also have to make website for that app also. Like - facebook have app as well as website.

If, you want to build only app you should learn Java or Python for that.
Java is most widely used language for mobile apps.
If, you want to build both app as well as website you should learn nodejs, expressjs, reactjs and
If you use Nodejs then you can make website and as we all know that website contains 2 parts (i.e front end and back end). So, if you are using nodejs then your back end will be same for both app and website because you use API in nodejs that connect your front end and back end seperately.
So, for making app you only want front end language like react native.
Back end for app and website will remain same.
These are not very complex languages and you need about 3–5 months depends on your hard work to learn these languages.

What you have to do after this -

You should also know DBMS (Database Management System) concepts and DBMS languages. Like - Mysql, mongodb etc.
Once you are familiar with above topics you can easily make your app in 1–2 months.
Good option will be team work. You can make team of classmates/ friends in your college and divide the work among themselves.
This will also help you learn the experience that how work is divided and done in companies.
Buy the domain and hosting for your website and add your app to playstore.
Share the url of your website/app with your friends/relatives on social networking sites. Like - facebook/instagram/whatsapp.
It requires hard work, constant study, faith,time …