• A: True. Glycerol decomposes at its normal boiling point, so it is purified by vacuum distillation.
• B: False. Aniline is immiscible in water but can still be purified by steam distillation.
• C: True. Ethanol forms an azeotrope with water, making azeotropic distillation effective for separation.
• D: True. A pure organic compound exhibits the same melting point even when mixed with another sample of the same compound.