Wet-process acidulation:\nLeaching phosphate rock with strong ________ acid produces phosphoric acid in industrial practice.

Introduction / Context:
Phosphoric acid, the backbone of phosphate fertilizers, is most commonly made by wet-process acidulation of phosphate rock (apatite). Although sulphuric acid is the dominant industrial reagent, hydrochloric acid can also leach phosphate rock to produce phosphoric acid, with different downstream separation steps. Recognizing that more than one strong acid can be used is important in exam contexts and process awareness.

Given Data / Assumptions:

• Feed is apatite-rich rock phosphate.
• Strong acids considered: sulphuric (H2SO4) and hydrochloric (HCl).
• Goal: produce phosphoric acid (H3PO4) in liquid phase.

Concept / Approach:
In the classic wet process, rock phosphate reacts with sulphuric acid to yield monocalcium phosphate in an acid liquor and gypsum (CaSO4·2H2O) as by-product; the liquor is concentrated to phosphoric acid. Alternatively, hydrochloric acid can leach phosphate to form soluble calcium chloride and phosphate species; after appropriate separations, phosphoric acid is recovered. Hence, both sulphuric and hydrochloric acids can serve as strong-acid leachants to produce phosphoric acid from rock.

Step-by-Step Solution:
Identify target: H3PO4 via rock leaching.Map common route: H2SO4 wet process.Recognize alternate route: HCl leaching with different by-products and purification needs.Therefore, choose “either (a) or (b)”.

Verification / Alternative check:
Process literature documents H2SO4-based plants worldwide and HCl-based niche processes where by-product handling (e.g., CaCl2) and impurity profiles justify the route.

Why Other Options Are Wrong:
“Neither” contradicts established practice; nitrous acid is irrelevant to phosphate rock leaching.

Common Pitfalls:
Assuming only sulphuric acid is possible; exams may test recognition that HCl is also technically viable, albeit less common industrially.

Final Answer:
either (a) or (b)