can you please explain how to get the answer

Example: Water in equilibrium with atmospheric nitrogen (pN2=0.80atm) has a nitrogen concentration of 5.45104mol/L at 20C. Calculate Henry law's constant KH(atm) Answer. First we have to calculate the mol fraction of N2. Since we only give the pressure to two decimal places we can safely use for the density of water 1.00g/mL, so 1L=1000g=55.6molH2O. The mol fraction of N2 is: XN2= 5.45104/(5.45104+55.6), so we can of course neglect the moles of N2 in the denominator, and find XN2=9.8106. We are clearly in the limit of low XB. Now eq. 8.31 yields directly KB=8.2104atm. Compare to the value in "Elements" Table 6.1 p. 144: Atkins uses mol/m3 and kPa1, so it should be compared to our KB1 and the more common X and atm we use here, so the value seems different, but try the conversion