Homologous Series Definition

Steps:

• Recall that a homologous series consists of organic compounds with the same functional group and similar chemical properties.
• Note that successive members differ by a -CH₂- unit in their molecular structure.
• Evaluate each option against this definition to identify the accurate statement.
• Confirm B matches the standard definition without qualifiers or errors.

Why B is correct:

• By definition, members of a homologous series differ successively by a -CH₂- unit, allowing predictable trends in properties like boiling point.

Why the others are wrong:

• A: Unsaturated series (e.g., alkenes) follow the same -CH₂- difference but are not distinguished this way; the rule applies generally.
• C: Structural isomers share the same molecular formula but have different structural formulas; displayed formulas vary too.
• D: The general formula for carboxylic acids is CₙH₂ₙO₂ (or RCOOH), not just CH₃COOH, which is a specific member.

Final answer: B