What grades would i get?

Hi, i have a feeling that i didn't really do my chemistry exam well..
so theoretically, if i get like a C/D in my AS chemistry overall and then get like a B / A in my overall A2..What final grade would i get?

That absolutely depends on your UMS. In the absolute worst case scenario that you get a low D at AS and a low B at A2, you'll get a C overall. In the absolute worst best case scenario that you get a high C at AS and a high A at A2, you'll get a borderline A/B overall. In a middle scenario where you get a borderline C/D at AS and borderline A/B at A2, you'll get a borderline C/B overall.