Is a commerce student eligible to pursue Bachelor of IT and Bachelor of computer applications courses?

Yes, commerce students too can pursue BCA without any problem. The general eligibility criteria for getting admission into BCA is that the candidate must have scored atleast 45% in their +2 board exams. This criteria differs from university to university, so you might have to consider a university w

As far as BCA is concerned, yes, you are eligible to do BCA but remember at the same time most of the institutes require maths/computer science at XII level. If you have one of them as your optional subject then you are good to go.