To calculate the density of sodium chloride NaCl at 25C and 1 atm, we need to find the mass of NaCl in one unit cell and divide it by the volume of the unit cell.First, let's determine the number of NaCl formula units in one unit cell. In a face-centered cubic FCC crystal structure, there are 4 formula units per unit cell. This is because there is 1/8 of an atom at each of the 8 corners and 1/2 of an atom on each of the 6 faces: 8 corners 1/8 + 6 faces 1/2 = 1 + 3 = 4 formula unitsNow, let's find the mass of NaCl in one unit cell. We know the molar mass of NaCl is 58.44 g/mol, so the mass of 4 formula units is: 4 formula units/unit cell 58.44 g/mol = 233.76 g/molNext, we need to find the volume of the unit cell. The unit cell edge length is given as 5.64 angstroms . To convert this to cm, we can use the conversion factor 1 = 1 10^-8 cm:5.64 1 10^-8 cm/ = 5.64 10^-8 cmNow, we can calculate the volume of the unit cell:Volume = edge length ^3 = 5.64 10^-8 cm ^3 = 1.79 10^-22 cmFinally, we can calculate the density of NaCl:Density = mass/volume = 233.76 g/mol / 1.79 10^-22 cm = 2.17 g/cmSo, the density of sodium chloride NaCl at a temperature of 25C and a pressure of 1 atm is approximately 2.17 g/cm.