1. The problem statement, all variables and given/known data 2. Relevant equations I have question for (a) section. 3. The attempt at a solution I have two answer for the question but I can't figure out which one is right. (1)Since the partition function is to sum up all the state in the system, I write down the answer (2)In other point of view, we can first find out the partition function of one O2 molecule. (either bound or unbound) And then, since a hemoglobin can only bind four O2 molecules, I can write down In my opinion, I think the first solution is more accurate since I include all the situation of that system. However, I cannot persuade myself that the second solution is wrong.(Or the reason is that Z=[Z1]N can only apply to large system?) Please help me out~ Thanks!!!!!!