Q.78
ICAR AIEEA PG Physical Science 09 July 2023 (Shift 1) Paper
MCQ (Single Correct) +4 −1
English हिन्दी

Phosphorus is immobile in soil because:

(A) Phosphate ions are held by anion exchange
(B) Phosphate ions are held by ligand exchange
(C) Phosphate ions are adsorbed as sparingly soluble phosphates of $\text{Fe/Al/Ca}$
(D) Phosphate ions are leached as completely soluble phosphates of $\text{Fe/Al/Ca}$

Choose the correct answer from the options given below:
1. (A), (B) and (C) only
2. (B), (C) and (D) only
3. (A), (B), (C) and (D)
4. (A), (C) and (D) only

फॉस्फोरस मृदा में गतिहीन (immobile) होता है क्योंकि:

(A) फॉस्फेट आयन ऋणायन विनिमय (anion exchange) द्वारा धारित होते हैं
(B) फॉस्फेट आयन लिगैंड विनिमय (ligand exchange) द्वारा धारित होते हैं
(C) फॉस्फेट आयन $\text{Fe/Al/Ca}$ के अल्प विलेय फॉस्फेट के रूप में अधिशोषित होते हैं
(D) फॉस्फेट आयन $\text{Fe/Al/Ca}$ के पूरी तरह विलेय फॉस्फेट के रूप में निक्षालित होते हैं

नीचे दिए गए विकल्पों में से सही उत्तर का चयन कीजिए:
1. केवल (A), (B) और (C)
2. केवल (B), (C) और (D)
3. (A), (B), (C) और (D)
4. केवल (A), (C) और (D)

EXPLANATION Soil Phosphorus Dynamics: P Fixation, Retention, Adsorption Isotherms, Labile P and Release

Phosphorus is notoriously immobile in soil environments due to:

  • Non-specific anion exchange on positively charged edge sites of kaolinite and oxides.
  • Specific adsorption via ligand exchange where phosphate oxyanions replace surface hydroxyl ($-\text{OH}$) groups on iron and aluminum hydrous oxides, forming stable binuclear inner-sphere complexes.
  • Precipitation as sparingly soluble iron/aluminum phosphates (variscite, strengite) in acidic soils, and calcium phosphates (hydroxyapatite, fluorapatite) in alkaline soils.
  • Statement (D) is incorrect because phosphates form sparingly soluble compounds and do NOT leach as completely soluble species.
Therefore, (A), (B) and (C) only are correct.

मृदा में फास्फोरस की गतिहीनता के कारण:

  • ऋणायन विनिमय द्वारा धनावेशित सतहों पर जुड़ना।
  • लिगैंड विनिमय (Ligand exchange) द्वारा Fe और Al ऑक्साइडों के साथ स्थिर आंतरिक-मंडल संकुल बनाना।
  • अम्लीय मृदाओं में Fe/Al और क्षारीय मृदाओं में Ca के अल्प विलेय यौगिकों के रूप में अवक्षेपित होना।
  • कथन (D) गलत है क्योंकि फास्फेट अत्यधिक अघुलनशील होते हैं और निक्षालित (leach) नहीं होते।
अतः केवल (A), (B) और (C) सही हैं।
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