Answer :
You need to first consider the properties of ethanoic acid that are worth noting. Ethanoic acid is a weak acid (the carboxyl group has a resonance-stabilized base), and the length of its carbon chain (2 carbons) reflects the strength of its Van der Waals forces. Also, the hydroxyl group (as part of the carboxyl group) confers a large dipole moment to the compound. The most similar compound would be the one that resembles ethanoic acid in these respects.
Thus, I would say that the answer is (2) C2H5OH. Because oxygen is highly electronegative, it can retain an extra electron without much difficulty, making the hydroxyl group slightly acidic. The hydroxyl group also confers a large dipole moment, and the 2 carbon backbone indicates similar Van der Waals interactions.
The correct answer is : (1) C3H7COOH.
Ethanoic acid has the molecular formula CH3COOH. It belongs to the homologous series of alkanoic acid or carboxylic acid. Homologous series are series of organic compounds in which a member differs from the next member by –CH2. One of the major characteristics of the homologues is their similarity in chemical properties. Propanoic acid (C3H7COOH) is the only member of the alkanoic acid family among the options given. So, it is the only one that has similar chemical properties with ethanoic acid. The other options are wrong because:
(2) C2H5OH belongs to the alcohol family.
(3) C2H5COOC2H5 belongs to the alkanoates family (esters)
(4) C2H5OC2H5 belongs to the ether family.
