Compound 'A' is ethanol 'C2H5OH'
Compound 'B' is ethanoic acid 'CH3COOH' which can be also write as C2H4O2
B cannot be aldehyde because final oxidation product is carboxylic acid but if oxidation is carried out in presence of some mild oxidising agent, then it may results aldehyde.
C2H5OH + O2 (strong oxidising agent) ------> CH3COOH + H2O
C2H5OH + O2 (weak/mild oxidising agent, PCC) ------> CH3CHO + H2O