Question

How many moles of $H_{3}P{O}_4$ are obtained by hydrolysing two moles of $P_4{O}_8$?

Answer 1

$P_4{O}_8+4H_{2}O\to 2H_{2}P{O}_3+2H_{3}P{O}_4$

One mole of $P_4{O}_8$ gives two moles of $H_{3}P{O}_4$, so 2 moles would give four moles.