Answer:
13 atoms
Explanation:
Look at the subscripts.
“Mg₃” means that there are 3 magnesium atoms; “PO₄” means that there is 1 phosphorus atom and 4 oxygen atoms. But note that the PO₄ group has a subscript too: 2. This multiplies the atom count by 2, so you have 2 phosphorus atoms and 8 oxygen atoms.
3 + 2 + 8 = 13
(hope this helps can i plz have brainlist :D hehe)