Some fertilisers are described as NPK fertilisers because they contain three elements needed for healthy plant growth: nitrogen ($N$), phosphorus ($P$), and potassium ($K$).

Which two of the following compounds each contain two of these three elements?

• Ammonium sulfate
• Ammonium phosphate
• Calcium nitrate
• Calcium phosphate
• Potassium chloride
• Potassium phosphate

Phosphate rock (containing calcium phosphate) is insoluble and must be treated with acids to produce soluble salts that can be used as fertilisers.

Name the soluble salts or fertiliser mixture produced when phosphate rock reacts with:

1. nitric acid
2. sulfuric acid