1. The problem statement, all variables and given/known data The atomic site that is in thermal and diffusive equilibrium with a gas of Helium atoms that is on the surface of a metal can either absorb an atom of Helium or it can be vacant. (a) What is the Grand Partition function of the system? (b) Derive the average thermal occupancy <N> of a site 2. Relevant equations 3. The attempt at a solution I have no idea where to even begin!