• Urea Hydrolysis Mechanism: Applied urea [$\text{CO(NH}_2)_2$] undergoes enzymatic hydrolysis by the soil enzyme urease to form ammonium carbamate, which rapidly breaks down into ammonium ions ($\text{NH}_4^+$), bicarbonate, and hydroxyl ions ($\text{OH}^-$).
• Normal Neutral Soils: Under favorable moisture and microbial urease activity in neutral soils ($pH\ 6.5–7.5$), urea hydrolysis proceeds rapidly and completes within 2 to 3 days.
• Alkaline / Calcareous Soils: In high pH calcareous/alkaline soils ($pH \gt 8.0$), high initial hydroxyl concentration and osmotic shifts retard optimal urease kinetics and promote intermediate carbonate precipitation, extending complete hydrolysis to about 7 days. (Correct answer: Option 4)

• Slurry Formation (A): Powdered rock phosphate (containing 30%–38% total $P_2O_5$) is reacted with sulfuric acid (65%–75% $H_2SO_4$) in an acidulator to produce soluble monocalcium phosphate and calcium sulfate.
• Denning Process (C): The reacting slurry is discharged into a den where solidification, continued acidulation, and initial crystallization of monocalcium phosphate occur over 0.5 to 4 hours.
• Curing (B): The solidified porous superphosphate mass is excavated and transferred to storage piles for 2 to 6 weeks of curing, allowing slow chemical reactions to reach equilibrium and excess free acid/moisture to dissipate.
• Granulation (D): If granular SSP is required, the cured or uncured powder can be granulated with water/steam in a rotary drum granulator.
• Conclusion: All operations (A), (B), (C), and (D) are integral components of single superphosphate manufacture. (Correct answer: Option 3)

• Photometric Accuracy & Beer-Lambert Law: In UV-Vis spectrophotometry, photometric accuracy and reproducibility depend on maintaining transmission within the optimal linear dynamic range where the relative error in concentration measurement is minimized.
• Ideal Absorbance Range: The optimal absorbance range for analytical measurement is 0.2 to 0.8 (corresponding to ~15% to 65% transmittance), where spectrophotometric detector noise and stray light errors are minimal. (Correct answer: Option 4)

• Equivalent Acidity of Ammoniacal Nitrogen Fertilizers:
• Equivalent acidity is defined as parts by weight of calcium carbonate ($ ext{CaCO}_3$) required to neutralize the acid-forming residual effect of $100$ parts of fertilizer:
• Ammonium Nitrate: Equivalent acidity $\approx 60$ $\rightarrow$ (C)
• Ammonium Sulphate Nitrate: Equivalent acidity $\approx 93$ $\rightarrow$ (D)
• Ammonium Sulphate: Equivalent acidity $\approx 110$ $\rightarrow$ (A)
• Ammonium Chloride: Equivalent acidity $\approx 128$ $\rightarrow$ (B)
• Correct Sequence of Increasing Equivalent Acidity: Ammonium nitrate ($60$) $\lt $ Ammonium sulphate nitrate ($93$) $\lt $ Ammonium sulphate ($110$) $\lt $ Ammonium chloride ($128$).
• Conclusion: Sequence is (C), (D), (A), (B), corresponding to Option 2.

Correct option: (2) (C), (D), (A), (B).