Hello student,
Popoff's rule states that during the oxidation of an unsymmetrical ketone, the cleavage of the C-CObond is such that the keto group always stays with the smaller alkyl group.
So, theoxidation product of CH3COCH(CH3)2 with HNO3 is two molecules of CH3COOH and HCOOH.
Regards
IHE