Hardness is the answer I believe
I think your anwser would be all of the above but you don't have it
Increase in carbon dioxide in your red blood cells which causes a drop in PH causes your breathing to speed up. If you hold your breath, rising carbon dioxide blood gas changes first leading to the urge to breathe. Carbon dioxide enters blood at the abdominal organs, hindlimbs, capillaries of the head.
Elements that have atoms with full outer shells of electrons
Are inert