What is the chemical formula for zinc phosphate?

First, we have to find the chemical formula for zinc ion and phosphate ion.

Zinc ion is a cation, and its formula is Zn^2+,
This is because zinc atom requires 2 outer shell electrons to be removed in order to become stable.

On the other hand, phosphate ion is a anion, and its formula is PO4^3-.

In order to find the chemical formula of this ionic bond, we need to make sure their charges are balanced.

To do this, take 2+ and 3-, their least common multiple is 6, so in order to turn both charges into 6+ and 6-, we need to determine how many of that ion is needed.

So to make 2+ to 6+, we need 3 zinc ions ( +2 x 3 = 6).
And to make 3- to 6-, we need 2 phosphate ions (-3 x 2 = - 6).

Now we can just combine the chemical formulas with the number of that ion needed (you can ignore the charge)
Therefore, your answer should be Zn3(PO4)2.

It shows that the experiment is designed properly.