The availability of P2O5 is maximum at

Answer: Option C

The availability of P₂O₅ is maximum at neutral pH.
P₂O₅ is listed as 'available phosphate'. The sum of the water-soluble and citrate-soluble phosphate is considered to be the amount of phosphate available to the plant and is the amount guaranteed on the fertilizer label.
In acidic soil, phosphorus reacts with iron and aluminum and makes it unavailable to plants.
Soil with inherent pH values between 6 - 7.5 is ideal for the availability of P₂O₅. Whereas pH values below 5.5 and between 7.5 - 8.5 limit phosphorus availability.