• Calcium Requirement in Legumes: Leguminous crops (Fabaceae) have a significantly higher physiological calcium ($Ca^{2+}$) requirement than graminaceous cereals and grasses.
• Physiological Roles: Calcium is indispensable for root hair curling, infection thread formation, and nodulation by Rhizobium bacteria, as well as synthesizing calcium pectate in the middle lamella of rapidly expanding root and pod tissues (e.g., preventing "pops" in groundnut).
• Cation Exchange Capacity (CEC): Legume roots possess high root CEC (~40–60 cmol/kg) with strong affinity for divalent cations like $Ca^{2+}$, whereas cereal roots have much lower root CEC (~10–25 cmol/kg). (Correct answer: Option 2)

• Bordeaux Mixture Composition: A protective contact fungicide discovered by Pierre-Marie-Alexis Millardet in France (1885) to control downy mildew (Plasmopara viticola) in grapes.
• Chemical Formulation: Prepared by reacting copper sulfate ($CuSO_4 \cdot 5H_2O$) with quicklime ($CaO$) or hydrated slaked lime [$Ca(OH)_2$] in water, typically in a 5:5:50 (or 1%) ratio, precipitating insoluble basic copper sulfates. (Correct answer: Option 3)

• Quantitative Volumetric Analysis Titrations and Chemical Indicators:
• Precipitation Titration: Uses Potassium chromate ($ ext{K}_2 ext{CrO}_4$) in Mohr's method (forming red $ ext{Ag}_2 ext{CrO}_4$) or Ferric alum in Volhard's method $\rightarrow$ (IV)
• Neutralization (Acid-Base) Titration: Uses pH indicators such as Thymolphthalein and Bromophenol blue $\rightarrow$ (III)
• Adsorption Indicator Titration (Fajans Method): Uses anionic dye indicators such as Fluorescein and Eosin that adsorb at the isoelectric equivalence point $\rightarrow$ (I)
• Oxidation-Reduction (Redox) Titration: Uses redox indicators such as Ferroin (1,10-phenanthroline iron(II)) and Diphenylamine $\rightarrow$ (II)
• Systematic Match: (A)-(IV), (B)-(III), (C)-(I), (D)-(II) corresponds to Option 4.

Correct option: (4) (A) - (IV), (B) - (MN), (C)~ (), (B) - (HN)