Answer: 13 atoms.
Step-by-step explanation:
The symbol for barium phosphate is Ba3(PO4)2. In 1 formula unit of barium phosphate there are 3 atoms of barium (Ba) (2)(1) = 2 atoms of phosphorus (P) (2)(4) = 8 atoms of oxygen (O) The total is 3 + 2 + 8 = 13 atoms.