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

1. Convert grams to moles:

* Molar mass of NaCl: 58.44 g/mol (approximately)

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

2. Calculate the 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 approximately 0.5005 M (molar).