In combination with a relative molecular weight of 80, the content of elements

In combination with a relative molecular weight of 80, the content of elements: 1.25% H, 38.75% P and 60.0% O. make up the molecular formula of this compound.

Let us write out the relative atomic masses of the elements: hydrogen is equal to 1, phosphorus is equal to 31, oxygen is equal to 16.
Let’s find the molecular weight of hydrogen in the compound:
80 * 0.0125 = 1 g / mol; (in compound 1 hydrogen atom)

Let’s find the molecular weight of phosphorus in the compound:
80 * 0.3875 = 31 g / mol; (in compound 1 phosphorus atom)

Let’s find the molecular weight of oxygen in the compound:
80 * 0.6 = 48 g / mol; (in the compound there are 3 oxygen atoms)

Answer: the molecular formula of the substance HPO3.