If an ion of an element is smaller than an atom of the same element then the ion has what charge?

the ion has a positive charge

Explanation: when a metal gives out electrons to form metallic ion, the resulting metal ion will be smaller compared to the metal atom because the metal will give out all its valence electron and in doing so, the metal will loss a shell of electron, thereby making it smaller when compared to the metal atom

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.