Phosphate availability is maximum in the pH range of

Correct option is A

The correct answer is (A) 6.5 – 7.5

Explanation:
• Phosphorus ($P$) is notorious for being the least mobile and most "fixed" nutrient in the soil.
• At low pH (acidic soil), phosphorus reacts with Iron ($Fe$) and Aluminum ($Al$) to form insoluble phosphates, making it unavailable to plants.
• At high pH (alkaline soil), phosphorus reacts with Calcium ($Ca$) to form insoluble calcium phosphates (apatites).
• The "sweet spot" where phosphorus fixation is minimized and availability is maximum is in the near-neutral range of 6.5 to 7.5.
• In this range, phosphorus primarily exists as the $HPO_4^{2-}$ and $H_2PO_4^-$ ions, which are easily absorbed by roots.

Information Booster:
• Mycorrhizal fungi are essential for helping plants scavenge phosphorus outside the narrow depletion zone around roots.
• Rock phosphate is an effective fertilizer in acidic soils but ineffective in neutral or alkaline soils.
• Most other macronutrients ($N$, $K$, $S$, $Ca$, $Mg$) also show high availability in the 6.5-7.5 pH range.

Additional Knowledge:
• Micronutrients: Unlike P, most micronutrients (Iron, Zinc, Manganese) are more available in acidic soils and become deficient in alkaline soils (except Molybdenum).
• Liming: Adding lime to acid soils is done specifically to raise the pH to this target range to unlock phosphorus.