Question

How many ions of hydrogen are there in 1.6moles of tetraoxophos phate(v) acid?

Answer 1

Is that H3PO4. Can't tell from the screwy name. Just get simple and call that phosphoric acid. That is a correct IUPAC name for it.

You have 1.6 mols H3PO4; therefore, you have
1.6 x 10^23 molecules of H3PO4.
There will be 3 times that for the number of H ions (assuming of course that all of them have ionized) because you have 3 H atoms for each molecule of H3PO4.