A flat graphite surface is in contact with a reserwir of gas molecules at a tixed chemical potential. There are M sites on the graphite surface on which gas molecules can adsorb, each sire can adsorb only a single molecule, and the adsorbed molecules do not interact with each other. Stanting from the grand canonical partition function, develop an expression for the coverage $-$ that is$,$ the fraction of the adsorption sites that are occupied $($contain an adsorbed gas molecule$)$ as a function of the chemical potential of the gas molecules in the reservoir.