Here's how to break it down:

* Sodium (Na): Sodium is a Group 1 element, meaning it has a +1 charge.

* Phosphite (HPO₃²⁻): Phosphite is the anion derived from phosphorous acid (H₃PO₃), which has a -2 charge.

To balance the charges, you need two sodium ions (2 x +1 = +2) to neutralize the -2 charge of the phosphite ion. This gives us the formula Na₂HPO₃.