chemistry amount of substance question

Which compound needs the greatest amount of oxygen for the complete
combustion of 1 mol of the compound?
A ethanal
B ethanol
C ethane-1,2-diol
D methanol
the answer is B but idk why?

Try writing out the formulae of each compound first:
A: CH3CHO (Mr = 44)
B: CH3CH2OH (Mr = 46)
C: HOCH2CH2OH (Mr = 62)
D: CH3OH (Mr = 32)
The more oxygen already present in each molecule, the less oxygen it will need to be completely combusted, so you are looking for the substance with the lowest percentage oxygen by mass.
Percentage by mass of oxygen = (number of oxygen atoms per molecule x Ar of oxygen)/(Mr of molecule) x 100%
A: (1 x 16)/(44) x 100% = 36.36…%
B: (1 x 16)/(46) x 100% = 34.78…%
C: (2 x 16)/(62) x 100% = 51.61…%
D: (1 x 16)/(32) x 100% = 50%
The percentage by mass of oxygen in ethanol is the smallest and so it needs the most oxygen to combust.
Alternatively, you could write balanced equations for the complete combustion of all of the compounds listed, but that would probably take you longer to do and so this is a quicker way.