What noble metal is most oxidation resistant?
Ruthenium, Rhodium, Palladium, Osmium, Iridium, Platinum, Gold


  ... I will narrow this question down to oxidation by diatomic oxygen in air at room and elevated temperatures.


According to this criterion, gold is the most oxidation resistant of the above metals.

First of all, gold oxide cannot be obtained by reaction of gold and oxygen ($\ce{O2}$) at standard pressure. Gold oxide ($\ce{Au2O3}$) decomposes to gold and oxygen above $\pu{160°C}$.


Ruthenium reacts with oxygen (air) above $\pu{700°C}$ to give $\ce{RuO4}$. Ruthenium powder burns in air.
Rhodium reacts with oxygen (air) above $\pu{700°C}$ to give $\ce{Rh2O3}$.
Palladium powder burns in air.
Osmium powder reacts with oxygen (air) at room temperature to give $\ce{OsO4}$.
Iridium reacts with oxygen at high temperatures to give $\ce{IrO2}$ or $\ce{IrO3}$. Iridium powder burns in air.
Platinum powder burns in air.