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

1. Calculate the moles of sodium hydroxide (NaOH)

* Molar mass of NaOH: 22.99 g/mol (Na) + 16.00 g/mol (O) + 1.01 g/mol (H) = 40.00 g/mol

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

2. Calculate the molarity

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

* Liters of solution: 0.500 L (given)

* Molarity: (2.00 mol NaOH) / (0.500 L solution) = 4.00 M

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