Answer:
The reason is because Flagstaff is at a higher elevation than Phoenix.
Explanation:
The air is thinner at higher elevations. You can google Flagstaff's elevation compared to Phoenix but the simple answer is that air is thinner at higher elevations and some people used to 'thicker' air find it harder to breath, especially after some strenuous exercise.
The answer is Independent Variable
Billions of years ago, according to the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule. This spark of life was the seed of every living thing we see today (as well as those we no longer see, like dinosaurs). That simplest life form, through the processes of mutation and natural selection, has been shaped into every living species on the planet.
I would be difficult to remove an electron from a Noble or Inert Gas (also known as the group 8 or 0 elements). This is because they all have filled outermost shells and as such the outermost shell would be held tightly to the nucleus and as such make it difficult to remove. Examples Helium, Neon, Argon, Xenon, Krypton and Radon