The compound formed between sodium (Na) and selenium (Se) is sodium selenide (Na₂Se).

Here's why:

* Sodium is an alkali metal in group 1 of the periodic table. It has a +1 charge when it forms an ionic bond.

* Selenium is a nonmetal in group 16 of the periodic table. It has a -2 charge when it forms an ionic bond.

To balance the charges, two sodium atoms (+1 each) are needed for every one selenium atom (-2). This gives the formula Na₂Se.