Here's how to determine the correct ionic formula for Ca²⁺ and P³⁻:

1. Identify the Charges:

* Calcium (Ca) has a +2 charge (Ca²⁺).

* Phosphorus (P) has a -3 charge (P³⁻).

2. Find the Least Common Multiple (LCM):

* The LCM of 2 and 3 is 6.

3. Determine the Subscripts:

* To achieve a +6 charge, we need 3 calcium ions (3 x +2 = +6).

* To achieve a -6 charge, we need 2 phosphorus ions (2 x -3 = -6).

4. Write the Formula:

* The correct formula is Ca₃P₂.