Solution :
When $${P_2}{O_5}$$ $$\left( {{\text{or}}\,{P_4}{O_{10}}} \right)$$ is heated with water, it form orthophosphoric acid $$\left( {{H_3}P{O_4}} \right).$$
$${P_4}{O_{10}} + 6{H_2}O \to 4{H_3}P{O_4}$$
Releted MCQ Question on Inorganic Chemistry >> P - Block Elements
Releted Question 1
The reddish brown coloured gas formed when nitric oxide is oxidised by air is