In order to find this answer, first we need to know that in 1 mol of atoms/elements, we will have 6.022*10^23 molecules of this compound, now when can do the calculations to find out how many molecules there are in 6.5*10^24, for every calculation with the number of molecules in 1 mol, I recommend a scientific calculator
6.022*10^23 = 1 mol
6.5*10^24 = x moles
x = 10.8 moles