Nitrogen gas is absorbed on 20% surface sites. On heating N$$_2$$ gas evolved from sites and was collected at 0.01 atm and 298 K in a container of volume 2.46 cm$$^3$$. Find out the number of surface sites occupied per molecule of N, if the density of surface sites is $$6.023\times10^{14}/\mathrm{cm^3}$$ and surface area is 1000 cm$$^2$$.