The general molecular formula for carboxylic acid is CnH2n+1COOH.
In organic chemistry, a homologous series is a sequence of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched, or differ by molecular formula of CH2 and molecular mass of 14u.
Second homologue : CH3COOH
=C2H4O2
Hence, the answer is B.