Counting single bonds via structural formulas Steps:

• Recall structures: CH₄ is methane (C with 4 H); CH₃OH is methanol (C with 3 H and OH); CH₃COH is acetaldehyde (CH₃CHO, with C=O); CH₃CH₃ is ethane (C₂H₆).
• List single bonds (one shared electron pair only): exclude double bonds.
• Count for each: A has 4; B has 5 (3 C-H, C-O, O-H); C has 5 (3 methyl C-H, C-C, aldehyde C-H); D has 7 (6 C-H, C-C).
• Identify maximum: D has the most single bonds.

Why D is correct:

• Ethane's formula C₂H₆ requires 7 single bonds to satisfy valences, per covalent bonding rules.

Why the others are wrong:

• A: Only 4 C-H single bonds in tetrahedral methane.
• B: 5 single bonds total, fewer than ethane's 7.
• C: 5 single bonds, as C=O double bond excludes it from single bond count.

Final answer: D