Balancing combustion reactions for oxygen moles

Steps:

• Write general combustion: C_xH_yO_z + a O_2 → x CO_2 + (y/2) H_2O, where a = x + (y/4) - (z/2).
• For each of the four compounds, determine x, y, z from structure and compute a.
• Identify compounds where a = 9 exactly.
• Count: two compounds satisfy this.

Why B is correct:

• Exactly two compounds require 9 moles O_2, matching the stoichiometry from balanced equations.

Why the others are wrong:

• A: Underestimates; two compounds need 9 O_2, not one.
• C: Overestimates; only two, not three.
• D: Incorrect; not all four require 9 O_2.

Final answer: B