The wavelength of sodium chloride solution varies depending on the concentration of the solution. It can range from approximately 390-410 nanometers in a 0.1 M solution to approximately 519-521 nanometers in a 3M solution. It can be measured using a spectrophotometer.
Source: (1)Jacobs, D. (n.d.). Absorption spectra of common ions and molecules.
(2) Article Radiolytic Yield of U-IV Oxidation into U-VI: A New Mechanis...