Which pair consists of members of the same homologous series (same functional group, formulas differing by one or more CH2 units)?

A $CH X_{3} CHO$ and $CH X_{3} COCH X_{3}$
B $CH X_{3} CH X_{2} OH$ and $CH X_{3} OCH X_{3}$
C $CH X_{3} COOH$ and $HCOOCH X_{3}$
D $CH X_{3} COOH$ and $CH X_{3} CH X_{2} COOH$

Answer: D

Members of a homologous series have the same functional group and differ by CH2. Ethanoic acid and propanoic acid are both carboxylic acids and differ by CH2. HCOOCH3 is an isomer of CH3COOH, not a homologue. An aldehyde and a ketone, or an alcohol and an ether, have different functional groups.

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Which pair consists of members of the same homologous series (same functional group, formulas differing by one or more CH2 units)?

Answer: D

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