* Find the atomic weights:

* Sodium (Na): 22.99 g/mol

* Sulfur (S): 32.06 g/mol

* Multiply the atomic weights by the number of atoms in the formula:

* Na: 22.99 g/mol * 2 = 45.98 g/mol

* S: 32.06 g/mol * 1 = 32.06 g/mol

* Add the results together:

* 45.98 g/mol + 32.06 g/mol = 78.04 g/mol

Therefore, the molecular weight of Na₂S is 78.04 g/mol.