Well it matters If it touch with liquid or soild, if touched with liquid it is not call wet, but with soild yes because something dry will get went when touched with water but something wet will stay wet when touched with water.
M = mols of solute / L of solution
Convert .50 g Na to mols Na by dividing by 22.99 and then dividing that by 1.5, which gives you a 0.014 M solution.