Which of the following compounds produces phosphoric acid when it reacts with water?

Phosphoric acid (H₃PO₄) is an important oxyacid of phosphorus. Several phosphorus-containing compounds produce H₃PO₄ when they react with water due to hydrolysis or oxidation reactions.

1. 
   

   Phosphorus pentachloride (PCl₅):
   PCl₅ hydrolyzes in water to produce phosphoric acid and hydrochloric acid:

   
   

PCl5+4H2O→H3PO4+5HClPCl₅ + 4H₂O → H₃PO₄ + 5HClPCl5+4H2O→H3PO4+5HCl

This reaction occurs because water molecules attack the phosphorus atom, replacing chlorine atoms with hydroxyl groups.

2. 
   

   Phosphorus trioxide (P₂O₃):
   P₂O₃ reacts with water to produce phosphorous acid (H₃PO₃) first:

   
   

P2O3+3H2O→2H3PO3P₂O₃ + 3H₂O → 2H₃PO₃P2O3+3H2O→2H3PO3

Upon further oxidation (by oxygen in air), H₃PO₃ is converted into H₃PO₄.

3. 
   

   Phosphorus pentoxide (P₂O₅):
   P₂O₅ is highly hygroscopic and reacts vigorously with water to produce phosphoric acid:

   
   

P2O5+3H2O→2H3PO4P₂O₅ + 3H₂O → 2H₃PO₄P2O5+3H2O→2H3PO4

This reaction is highly exothermic and demonstrates the strong dehydrating nature of P₂O₅.

Because all these compounds eventually yield phosphoric acid when reacted with water (either directly or after oxidation), the correct answer is D) All of the above.

These reactions are fundamental in inorganic chemistry, illustrating the versatility of phosphorus compounds and their transformation into acids. Phosphoric acid produced from these compounds has widespread industrial applications, including fertilizers, food additives, and chemical synthesis.