Here's how to calculate the molarity of the sodium hydroxide solution:

1. Calculate the moles of NaOH:

* Molar mass of NaOH: 22.99 g/mol (Na) + 15.99 g/mol (O) + 1.01 g/mol (H) = 40.00 g/mol

* Moles of NaOH: (80 g) / (40.00 g/mol) = 2.00 mol

2. Convert volume to liters:

* Volume in liters: 500 mL / 1000 mL/L = 0.500 L

3. Calculate Molarity:

* Molarity (M) = moles of solute / liters of solution

* Molarity = 2.00 mol / 0.500 L = 4.00 M

Therefore, the molarity of the sodium hydroxide solution is 4.00 M.