ANS:B - sulphuric

The reaction of sulphuric acid with phosphate rock produces superphosphates. Explanation: Superphosphate fertilizers, which are commonly used in agriculture to supply phosphorus to plants, are produced by reacting phosphate rock with sulphuric acid. This reaction is known as the acidulation process. In the acidulation process:

• Phosphate rock (which primarily consists of calcium phosphate) is treated with concentrated sulphuric acid.
• The sulphuric acid reacts with the calcium phosphate in the rock to produce water-soluble forms of phosphorus, such as monocalcium phosphate and gypsum (calcium sulfate).
• The resulting mixture is then treated to remove impurities and adjust the nutrient content before being dried and granulated to form superphosphate fertilizers.

This process converts the relatively insoluble phosphorus in phosphate rock into more soluble forms that plants can readily absorb and utilize for growth. Superphosphates are valued for their ability to provide an immediate source of phosphorus to crops, promoting root development, flowering, and fruiting. Therefore, the reaction of sulphuric acid with phosphate rock is essential for the production of superphosphate fertilizers.