C5H10O methyl ketone isomers

Steps:

• NaBH4 reduction adds 2 u to molar mass; 2.32% increase gives Mr(X) ≈ 86 (exact for C5H10O).
• Iodoform test (yellow ppt with I2/OH-) indicates methyl ketone (CH3COR).
• For C5H10O, R = C3H7 (two isomers: n-propyl, isopropyl).
• Yields pentan-2-one (CH3COCH2CH2CH3) and 3-methylbutan-2-one (CH3COCH(CH3)2); both acyclic with one carbonyl.

Why B is correct:

• Exactly two C3H7 isomers fit CH3COC3H7 formula for methyl ketones.

Why the others are wrong:

• A: Ignores two distinct C3H7 structures.
• C: No additional C5 methyl ketone isomers exist.
• D: Exceeds actual count of two.

Final answer: B