Hi

If open category seats remains vacant then,

The vacanct  open seat is alloted to   to the one who has the highest marks irrespective of the category he belongs, means no category / community is given preference

This is because,

There is no reservation for open category seats as they are unreserved.

For example,

If there's 1 vacant open seat,

And we have two candidates one is OBC with 200 marks and another is sc with 180 marks, then that vacant seat will be allotted to  the OBC candidate as that obc Candidate has higher marks than that of SC candidate.

Thank you