Is hostel compulsory at Imperial College of Engineering and Research?

ICOER is a completely residential college and students, specifically the girls are expected to stay in the on-campus hostels provided which consists of two hostels with common kitchens/mess.

But the boys are not provided with on campus accomodations and have to get private accomodation outside the ca

No, hostel accommodation is not compulsory at Imperial College of Engineering and Research. The college has a limited number of hostel rooms, and they are allocated on a first-come, first-served basis. If you do not get a hostel room, you will need to find private accommodation.