since, the compound reacts with Tollen's reagent so it must contain a - CHO (aldehyde) group. Further, it does not give aldol condensation, it means that in it, α -hydrogen atom(s) is (are) absent. The structure of the given compound is as
CH3
α
C
H2
O
||
C
−
α
C
H2CH3
3−pentanone
(No-CHO group but α−H atoms present )
CH3‌
α
CH3
|‌‌‌
CH
|‌‌‌
CH3
−CHO 2,2 -dimethyl propanaol (have - CHO group and no α−H atom is present) CH3−CH=
‌‌‌OH
|
C
−CH2CH3 3 -hydroxy-2-pentene (No - CHO group) CH3
CH3
|‌‌‌
CH
α
C
H2CHO 3 -methyl butanal (have - CHO group and α−H atom ) CH3
CH3
|‌‌‌
CH
−
O
||
C
−CH3 (No - CHO group and one α−H atom ) Thus, A is 2,2 -dimethylpropanal (as it contains a - CHO group but no α - H atom).