The ketone shown is treated with an excess of methylmagnesium bromide in dry ether, followed by aqueous acid work-up. To which class does the product belong?

Propanone (acetone) is a ketone, so one methyl group adds to the carbonyl carbon and gives a tertiary alkoxide. Protonation on work-up gives 2-methylpropan-2-ol, a tertiary alcohol (aldehydes give secondary alcohols, formaldehyde gives primary).