Here's how to calculate the relative atomic mass of phosphoric acid (H₃PO₄):

1. Identify the elements and their atomic masses:

* Hydrogen (H): 1.008 u

* Phosphorus (P): 30.974 u

* Oxygen (O): 15.999 u

2. Count the number of atoms of each element in the formula:

* H: 3 atoms

* P: 1 atom

* O: 4 atoms

3. Multiply the atomic mass of each element by its number of atoms:

* Hydrogen: 1.008 u/atom * 3 atoms = 3.024 u

* Phosphorus: 30.974 u/atom * 1 atom = 30.974 u

* Oxygen: 15.999 u/atom * 4 atoms = 63.996 u

4. Add the results to get the relative atomic mass of phosphoric acid:

* 3.024 u + 30.974 u + 63.996 u = 97.994 u

Therefore, the relative atomic mass of phosphoric acid (H₃PO₄) is approximately 97.994 u.