Given below are two statements: Statement (I): Humus is the... | Agrigyan

Biochemical functions of plant nutrients:

• Molybdenum (Mo): Vital structural component of nitrogenase (Fe-Mo protein in biological $N_2$ fixation) and nitrate reductase (converts $NO_3^-$ to $NO_2^-$): (A)-(III).
• Nickel (Ni): Essential metallic cofactor of the enzyme urease, catalyzing hydrolysis of urea to ammonia and carbon dioxide: (B)-(IV).
• Phosphorus (P): Integral part of ATP, ADP, and high-energy pyrophosphate bonds mediating metabolic energy transfer: (C)-(I).
• Magnesium (Mg): Central coordinated metal cation of the porphyrin ring in chlorophyll molecules: (D)-(II).

Luxury consumption in plant nutrition:

• Definition: Luxury consumption refers to the absorption and accumulation of a nutrient in excess of the physiological requirement for maximum growth without any corresponding increase in crop yield.
• Potassium ($K^+$) is the classic element exhibiting luxury consumption because plants rapidly take up soluble potassium far beyond sufficiency levels, storing it within cell vacuoles for osmotic regulation without proportional yield increases.
• Nitrogen, Calcium, and Sulphur are regulated much more strictly and do not typically exhibit classical luxury consumption without toxicity or vegetative overgrowth.

Option analysis:

• Acid sulfate soils (often called cat clays) are formed under waterlogged coastal or estuarine environments containing high amounts of iron pyrite ($FeS_2$).
• Upon drainage and oxidation, pyrite reacts with oxygen and water to produce sulfuric acid ($H_2SO_4$) and jarosite, causing soil pH to plummet drastically below $4.0$ (typically $pH \lt 3.5 - 4.0$).
• Consequently, the pH of acid sulfate soils is characteristically less than $5.0$.