$word_{count}$: 200

Column Chromatography: Stationary = $\frac{alumina}{silica}$ gel in glass column. Mobile = organic eluent (gradient: hexane → ethyl acetate → methanol). Principle: adsorption. Non-polar compounds elute first (weak adsorption). Polar compounds need polar eluent (strong adsorption). Used for: plant pigments, drug purification, natural products. TLC (Thin Layer Chromatography): Same as column but faster, analytical scale. Stationary = thin silica layer on plate. Spots visualized by UV, iodine, or reagent spray. Rf = distance$\frac{spot}{distance}$(solvent front). Higher Rf = less polar. Used for: monitoring reactions, identifying compounds. Paper Chromatography: Stationary = WATER in cellulose fibers (NOT the paper itself). Mobile = organic solvent. Principle: PARTITION (not adsorption — this is the key distinction). Used for: amino acid separation (ninhydrin detection), food dye analysis. Gas Chromatography (GC): Stationary = liquid on inert solid. Mobile = inert carrier gas (He, N2). For volatile compounds. Partition-based. JEE critical points: Paper = partition (water stationary), TLC/Column = adsorption $\frac{silica}{alumina stationary}$. Rf interpretation (high = non-polar on silica). Choice of eluent polarity.