Homologous series in organic chemistry Steps:

• Recall that a homologous series contains compounds with the same functional group, similar properties, and molecular formulas differing by -CH₂- (general formula like CₙH₂ₙ₊₂ for alkanes).
• Analyze option A: Compounds are CH₃CH₂CH₃ (C₃H₈), CH₃CH₂CH₂CH₃ (C₄H₁₀), CH₃CH₂CH₂CH₂CH₃ (C₅H₁₂)—all saturated hydrocarbons (alkanes).
• Analyze option D: Compounds are CH₃CH₃ (C₂H₆), CH₃CH₂CH₃ (C₃H₈), CH₃CH₂CH₂CH₃ (C₄H₁₀)—also all alkanes.
• Confirm options B and C mix different functional groups (ethers, alcohols, acids), so no common series.

Why A and D are correct:

• Both sets follow the alkane general formula CₙH₂ₙ₊₂, with successive members increasing by one -CH₂- unit (n=3,4,5 for A; n=2,3,4 for D).

Why the others are wrong:

• B: Mixes ether (CH₃OCH₃), alcohol (CH₃CH₂OH), and carboxylic acid (CH₃COOH) from separate series.
• C: Mixes ether (CH₃CH₂OCH₃), alcohol (CH₃CH₂OH), and carboxylic acid (CH₃COOH) from separate series.

Final answer: A and D