Hi Shubham,

Seats that remain vacant after direct admission are filled by conducting  written test and/or interview/ spot admissions.

IIT Bombay takes out its minimum qualifying criteria for spot round in an advertisement that is available in leading newspapers and on IIT website. But since the pool of candidates for spot round admission is huge, and this makes it difficult for the departments to conduct written tests/interviews for all of them. So they limit the number of candidate with eligibility criteria higher than that of the  minimum prescribed in the advertisement.