Answer: 12 ( answer not among the option)
Explanation:
From the equation of reaction; P4O10+ H2O -----> H3PO4, it is unbalanced.
One can only get the exact number of ''Hydrogen atom'' if it is well balanced.
Adding '4' to H3PO4 on the RHS and '6' to H2O on LHS of the equation would give a balanced equation such as;
P4O10 + 6H2O -----> 4 H3PO4
Therefore the number of hydrogen atoms found on the reactant is 12.
