Answer is C Size-exclusion--or gel filtration--chromatography separates proteins based on their Stokes radius, the radius of the sphere they occupy as they tumble in a solution. The stokes radius is a function of molecular mass and shape. When rapidly tumbling, an elongated protein occupies a larger effective volume than a spherical protein of the same mass. Size-exclusion chromatography employs porous beads. Ref: Harper's Illustrated Biochemistry, 30E (2015) Pg No 27. in Ion Exchanege chromatography ,Cation-exchange solid phases contain covalently bound, negatively charged functional groups. Examples include strongly acidic groups, such as sulfonate ions, or weakly acidic groups, such as carboxyl or carboxymethyl . Immobilized enzymes have been chemically bonded to adsorbents, such as (1) microcrystalline cellulose,(2) diethylaminoethyl (DEAE) cellulose, (3) carboxymethyl cellulose, and (4) agarose. Ref: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 5E Pg no 308 and 375 Iso Electric focussing is based on electric field and pH. Ionic buffers called ampholytes and an applied electric field are used to generate a pH gradient within a polyacrylamide matrix. Applied proteins migrate until they reach the region of the matrix where the pH matches their isoelectric point (pI). Ref: Harper's Illustrated Biochemistry, 30E (2015) Pg No 29.