The answer is strontium dihydrogen phosphate
That is strontium dihydrogen phosphate, is the compound containing the most hydrogen atoms per molecule or formula unit.
The formulas of the following compounds are as follows:
Hydrogen selenide H₂Se
Ammonium bromide NH₃Br
Strontium dihydrogen phosphate Sr(H₂PO4)₂
Sodium bicarbonate NaHCO₃
As it can be seen from the formula of strontium dihydrogen phosphate Sr(H₂PO4)₂ , that it contains the most hydrogen atoms per molecule or formula unit.