To determine the concentration of iron II ions in the water sample, we need to use the Beer-Lambert Law, which states that the absorbance A of a solution is directly proportional to its concentration c and path length l through which the light passes:A = * c * lWhere:A = absorbance 0.345 in this case = molar absorptivity also known as molar absorption coefficient in L/ mol*cm c = concentration in mol/Ll = path length in cm usually 1 cm for standard cuvettes However, we need the concentration in mg/L, not mol/L. To convert between these units, we need the molar mass M of iron II ions Fe :c mg/L = c mol/L * M mg/mol First, we need to find the molar absorptivity for the 1,10-phenanthroline method at a wavelength of 477 nm. This value is typically determined experimentally and should be provided in the literature or the instrument manual. If you don't have this value, you can create a calibration curve using a series of standard solutions with known concentrations of iron II ions and measure their absorbance at 477 nm. Then, plot the absorbance values against the concentrations and find the slope of the linear regression line, which represents the product of and l * l .Once you have the value of * l, you can calculate the concentration of iron II ions in mol/L using the Beer-Lambert Law:c mol/L = A / * l Next, convert the concentration from mol/L to mg/L using the molar mass of iron II ions Fe . The molar mass of iron is 55.845 g/mol:c mg/L = c mol/L * M mg/mol By plugging in the values and performing the calculations, you will get the concentration of iron II ions in the water sample in mg/L.