Which quantity is most closely related to the speed of gas particles

Temperature is a measure of the energy of molecules and energy is related to speed. 

The water in a pot is heated by convection. The water on the bottom will warm up and rise toward the surface and the cooler water will then sink to the bottom where it will be heated. 

Oxygen will form ionic bonds with nitrogen. The others will not by themselves. 

A high pH is indicative of a basic solution. HCl and H2SO4 are both strong acids and will result in a lower (more acidic) pH. Water is the standard. KOH is a strong base and will increase the pH. 

An acidic solid will lower the pH of a solution. pH measures the number of hydrogen ions and a lower pH will mean that there are more H+ ions, but the solid could just have reacted with the OH- to cause the pH to decrease