This question is about the raw materials used to manufacture monoammonium phosphate, a widely used phosphatic fertilizer.
- Phosphoric acid: neutralizing phosphoric acid with ammonia in a one to one mole ratio gives exactly monoammonium phosphate, \(NH_4H_2PO_4\). This is the correct raw material.
- Nitric acid: ammonia reacting with nitric acid gives ammonium nitrate, a nitrogen fertilizer with no phosphorus in it at all.
- Sulphuric acid: ammonia reacting with sulphuric acid gives ammonium sulphate, again a straight nitrogen and sulphur fertilizer, not a phosphate.
- Hydrochloric acid: ammonia reacting with hydrochloric acid gives ammonium chloride, a chloride salt with no phosphorus.
Only the reaction with phosphoric acid brings the phosphate group into the product, which is what makes it monoammonium phosphate in the first place.
Let's summarize:
- \(NH_3 + H_3PO_4 \rightarrow NH_4H_2PO_4\) is the reaction that forms monoammonium phosphate.
- Swapping in nitric, sulphuric or hydrochloric acid instead gives a different salt entirely, none of which contain phosphorus.
So the correct acid is phosphoric acid, option 1.