The carbonyl carbon in a ketone is attacked primarily by the peroxy oxygen bonded to hydrogen as opposed to the peroxy oxygen bonded to carbon because:

This is because peroxy oxygen bonded to hydrogen can easily undergo nucleophilic protonation with the carbonyl carbon to form an alcohol

Explanation:

A ketone is a functional group that contains a carbonyl group (carbon-oxygen double bond ( R1R2-C=O).

The carbonyl carbon doubly bonded to the oxygen is electron deficient as a result of difference in electronegativity between carbon and oxygen, hence is susceptible to nucleophilic attacks

R1R2 - C = O

where R1 and R2 are organic substituents.

The peroxy oxygen that is bonded to hydrogen (H -O-O-R) is the electron-rich centre and easily attacks electron-deficient centres like the carbonyl carbon in ketones to form an alcohol.

The bond between the hydrogen attached to the peroxy oxygen is broken and the resultant hydrogen ion undergoes protonation with the oxygen of the carbonyl group to form an alcohol

R1R2 - C = O + H - O-O - R =>

R1R2- CH - OH + R - O-O-R1