Two compounds A and B with same molecular formula (C?H?O) undergo Grignard reaction with methylmagnesium bromide to give products C and D. Products C and D show following chemical tests. C and D respectively are:

 

gives iodoform test and slow Lucas test, so it's a methyl secondary alcohol. D gives fast Lucas test, so it's a tertiary alcohol. The Grignard products must be tertiary and secondary alcohols. So A and B must be an aldehyde and a ketone.