All of the atoms of argon have the same

The answer to this question would be: Atomic number

The number of protons will determine the atomic number of an element and it should be same in different isotopes. Atomic mass is calculated by adding the number of protons with the number of neutrons. In isotopes, the amount of neutron will be different, causing the atomic mass of the element became different. 

Your question is not clear but if you can explain yourself i would be glad to .  just trying to : ))

Ibelieve it's temperature! i'm not 100% sure.