To calculate the BET surface area, we can use the following equation:BET surface area = Amount of adsorbed gas * Molecular cross-sectional area of adsorbate / Monolayer coverageFirst, we need to convert the amount of adsorbed gas from mmol to mol:7.2 mmol * 1 mol / 1000 mmol = 0.0072 molNext, we need to find the molecular cross-sectional area of nitrogen gas. The cross-sectional area of a nitrogen molecule can be estimated as 0.162 nm^2. To convert this to m^2, we can use the following conversion:0.162 nm^2 * 1 m / 1 x 10^9 nm ^2 = 0.162 x 10^-18 m^2Now, we can plug these values into the BET surface area equation:BET surface area = 0.0072 mol * 0.162 x 10^-18 m^2 / 5.8 x 10^-7 mol/m^2 BET surface area = 1.1664 x 10^-20 m^2 / 5.8 x 10^-7 m^2/mol BET surface area = 2.011 x 10^13 m^2/molSince we are looking for the surface area of the sample, we can multiply this value by the amount of adsorbed gas 0.0072 mol :Surface area = 2.011 x 10^13 m^2/mol * 0.0072 molSurface area 1.448 x 10^11 m^2So, the BET surface area of the sample of carbon adsorbent is approximately 1.448 x 10^11 m^2.