For getting a seat in government college, for MBBS your score should be no less than 450. The cut-off for ST candidates is 40th percentile of the highest marks scored. So if the topper scores suppose 600, the cut off would be 40th percentile of that score. 
Again, the scores and the cut-offs will vary depending upon the college and the state of domicile. I have only given you an overall view of cutoffs.