Here's how to calculate the concentration of the NaCl solution:

1. Calculate the number of moles of NaCl:

* Molar mass of NaCl: 58.44 g/mol

* Moles of NaCl: (58.5 g) / (58.44 g/mol) = 1.001 mol

2. Calculate the concentration (Molarity):

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

* Molarity: (1.001 mol) / (2 L) = 0.5005 M

Therefore, the concentration of the NaCl solution is 0.5005 M (or approximately 0.5 M).