• Purification and Separation of Macromolecular Proteins:
• Specialized biochemical separation techniques for proteins include:
• Chromatography: Ion-exchange, affinity, and hydrophobic interaction chromatography exploit specific surface charges and binding affinities.
• Iso-electric precipitation: Proteins carry zero net charge at their isoelectric point ($pI$), minimizing electrostatic repulsion and causing selective precipitation.
• Gel filtration: Size-exclusion chromatography separates protein molecules based on hydrodynamic molecular weight through porous dextran/agarose beads.
• (A) Decantation is a coarse gravity separation of macroscopic sediments, unsuitable for molecular-level protein fractionation.
• Conclusion: (B), (C) and (D) only (Option 4).

Correct option: (4) (B), (C) and (D) only.