Tertiary alcohols resist oxidation; smallest is tert-butanol

Steps:

• Tertiary alcohols cannot be oxidized by warm acidified KMnO4 due to no alpha hydrogen.
• Non-cyclic tertiary alcohols qualify; the smallest is 2-methylpropan-2-ol (C4H10O).
• Molecular mass of C4H10O is 74 g/mol, lowest among such alcohols.
• Combustion: C4H10O + 6 O2 → 4 CO2 + 5 H2O requires 6 mol O2 per mol alcohol.

Why C is correct:

• Balanced combustion equation for C4H10O yields exactly 6 mol O2, matching stoichiometry.

Why the others are wrong:

• A: 3.5 mol fits incomplete or erroneous balancing, ignoring full oxidation.
• B: 4.5 mol underestimates O2 for C4H10O's 4 C and 10 H atoms.
• D: 6.5 mol overestimates, possibly confusing with larger alcohols like pentanols.

Final answer: C