Here's how to determine the formula:

1. Identify the charges:

- Calcium (Ca²⁺) has a +2 charge.

- Arsenate (AsO₃⁻⁴) has a -4 charge.

2. Find the least common multiple (LCM) of the charges:

- The LCM of 2 and 4 is 4.

3. Determine the subscripts:

- To achieve a +4 charge, you need 3 calcium ions (3 x +2 = +6).

- To achieve a -4 charge, you need 2 arsenate ions (2 x -4 = -8).

4. Write the final formula:

- Ca₃(AsO₄)₂