ICAR AIEEA PG Physical Science 09 July 2023 (Shift 1) Paper

Nutrient mobility in soil is governed by electrostatic interaction with negatively charged soil colloids:
Mobile nutrients: Nitrate ($\text{NO}_3^-$) and Chloride ($\text{Cl}^-$) are monovalent anions that do not adsorb onto negative clay surfaces; Boric acid ($\text{H}_3\text{BO}_3$) exists as an uncharged neutral molecule in standard soil pH and moves freely with soil water.
Immobile/less mobile nutrients: Cations ($\text{Cu}^{2+}, \text{Fe}^{2+}, \text{NH}_4^+$) are strongly bound by cation exchange, and Phosphate ($\text{H}_2\text{PO}_4^-$) is strongly fixed by chemical precipitation and ligand exchange.

Weatherability refers to the susceptibility or ease with which a mineral undergoes chemical weathering:
Highly weatherable minerals: Olivine, Augite, Biotite.
Moderately resistant: Garnet, Feldspars, Muscovite.
Highly resistant (lowest weatherability): Quartz, Tourmaline, Zircon.
In sequence (A), the ferromagnesian minerals (Biotite/Augite) have far higher weatherability than Garnet, which in turn weathers faster than Quartz (the most resistant residual mineral). Thus (A) represents a valid descending order of weatherability.
Sequences (B), (C), and (D) incorrectly place ultra-resistant heavy minerals (Zircon, Tourmaline) as having higher weatherability than easily weatherable minerals like Olivine.

Formula for mass of solute required for a normal solution:

For Sodium Carbonate ($\text{Na}_2\text{CO}_3$):
Molar mass $M = (23 \times 2) + 12 + (16 \times 3) = 46 + 12 + 48 = 106\text{ g/mol}$
Valency factor $n = 2$ (since $2\text{ Na}^+$ or $\text{CO}_3^{2-}$)
Equivalent weight $E = \frac{M}{n} = \frac{106}{2} = 53\text{ g/eq}$
Given:
Normality $N = 0.1\text{ N}$
Volume $V = 500\text{ ml}$

Volumetric titration techniques:

• Complexometry (Complexometric titration): A volumetric technique based on the formation of stoichiometric, stable, soluble coordination complexes or chelates between metal ions and polydentate chelating ligands (such as EDTA) detected using metallochromic indicators (e.g., Eriochrome Black T).
• Precipitometry / Argentometry involves precipitation reactions (e.g., using $\text{AgNO}_3$).
• Thiocyanometry involves titration with thiocyanate ($ ext{SCN}^-$).

Matching concepts with their pioneering scientists:

• Justus von Liebig established mineral plant nutrition and is hailed as the 'Father of agricultural and fertilizer chemistry' -> (III).
• F.W. Parker et al. (1951) proposed the Nutrient Index concept to categorize fertility status of soils -> (IV).
• Stanley A. Barber formulated the mechanistic nutrient uptake model delineating root interception, mass flow, and diffusion -> (II).
• M.L. Jackson (1948) developed the classic weathering stages and chemical weathering index of clay-sized minerals -> (I).