No 'if' about it. It's the probability we use to calculate the entropy. Clearly, according to your logic, every single salt crystal in the world has been individually designed.
If it is cold enough to solidfy the Cl, and you make a dust of the solid phase Cl and Na so fine it is one atom grains and then mixed the Na and Cl together and magically came up with a salt cube of 1 gram, gee willikers your probability would be correct. That's ignoring van der walls and non-ionic bondings which I'm not running over to a chemistry book to look up. Is there a single atom Cl, or single atom Na in a solid dust form? That sounds strange. Maybe in a mass spectrometer, "vapor" deposition or something like that. But then the "intelligent designer" is very much in play -- that being the physical chemist and his toys.
As to the relation to entropy, you'll have to explain that more carefully in a bit more detail, I don't quite catch it.