The molecular formula C_3H_6OC3H6O which follows general molecular formula C_nH_(2n)OCnH2nO represents either a saturated aldhyde or a saturated ketone.A compound containing ketomethyl group (CH_3CO-CH3CO−) linked with H atom or hydrocarbon group responds to iodoform test and a compound containing -CHO−CHO group responds to Tollen's reagent.A reduces this reagent but B does not.So A contains -CHO−CHO group.Again B undergoes iodoform test but A does not.So it contains CH_3CO-CH3CO− group but not -CHO−CHO
So" "A->CH_3CH_2CHO->"propanal" A→CH3CH2CHO→propanal
and B->CH_3COCH_3->"propanone"B→CH3COCH3→propanone