Statement A: Glycerol is purified by vacuum distillation because it decomposes at its normal boiling point.

This statement is correct. Glycerol decomposes at its normal boiling point (290°C approximately), so vacuum distillation is used to lower the boiling point and prevent decomposition.

Statement B: Aniline can be purified by steam distillation as aniline is miscible in water.

This statement is incorrect. Aniline is not completely miscible in water. However, it can be purified by steam distillation due to its relatively high boiling point and water’s ability to carry it over as a vapor. The statement as given is not entirely correct.

Statement C: Ethanol can be separated from ethanol-water mixture by azeotropic distillation because it forms an azeotrope.

This statement is correct. Ethanol and water form a minimum boiling azeotrope, which has a constant boiling point lower than either pure component, enabling separation through azeotropic distillation.

Statement D: An organic compound is pure if the mixed melting point remains the same.

This statement is correct. If mixing a small quantity of an unknown compound with a known compound does not change the melting point, this suggests the unknown compound is the same as the known and thus pure.

Based on the analysis, the correct statements are A, C, and D.

Option A: A, C, D only.