M:M+1 ratio indicates number of carbon atoms from ¹³C isotope abundance

Steps:

• M+1 peak arises mainly from ¹³C substitution; relative abundance M+1/M ≈ n × 1.1%, where n = number of C atoms.
• Given ratio M:M+1 = 13:1, so M+1/M = 1/13 ≈ 0.077 (7.7%).
• Solve for n: 7.7% / 1.1% ≈ 7 carbon atoms.
• Eliminate A (C₄H₁₀, 4C) and B (C₆H₁₂O, 6C); both C and D are C₇H₁₆O (7C), but assess structure for observable M peak.

Why D is correct:

• 3,3-Dimethylpentan-1-ol has 7 C atoms; gamma-branching allows stable molecular ion, enabling accurate M:M+1 measurement per isotopic distribution formula.

Why the others are wrong:

• A: Butane has 4 C atoms; expected M:M+1 ≈ 91:1.
• B: Hexan-3-one has 6 C atoms; expected M:M+1 ≈ 15:1.
• C: 2,2-Dimethylpentan-1-ol has 7 C atoms, but beta-quaternary branching promotes facile fragmentation, yielding weak/absent M peak.

Final answer: D