Isotope pattern in mass spectrometry distinguishes halogens but ratio doesn't match

Steps:

• Identify halogens in choices: A and B contain Cl (isotopes 75% ³⁵Cl, 25% ³⁷Cl); C and D contain Br (50% ⁷⁹Br, 50% ⁸¹Br).
• Calculate expected M⁺2/M⁺ ratio for monohalides: for Cl, 25/75 = 0.33; for Br, 50/50 = 1.
• Compare to given ratio of 15: no choice matches, as 15 would require ~15 Br atoms via binomial distribution where M⁺2/M⁺ ≈ n for Br.
• Conclude data insufficient to identify specific compound.

Why D is correct:

• Not enough information.

Why the others are wrong:

• A: Cl gives M⁺2/M⁺ = 0.33, not 15.
• B: Cl gives M⁺2/M⁺ = 0.33, not 15.
• C: Br gives M⁺2/M⁺ = 1, not 15.

Final answer: Not enough information.