Here's how to determine the formula for the compound formed between sodium (Na) and nitride (N⁻³):

* Identify the Charges:

* Sodium (Na) is in group 1 of the periodic table, so it has a +1 charge (Na⁺).

* Nitride (N⁻³) has a -3 charge.

* Balance the Charges: To create a neutral compound, you need three sodium ions (Na⁺) to balance the charge of one nitride ion (N⁻³).

* Write the Formula: The formula for the compound is Na₃N.