It is now understood that the reason that inert gases are completely inert to basic chemical reactions -LRB- such as combustion , for example -RRB- is that their outer valence shell is completely filled with electrons .

No one knows that the reason that inert gases are completely inert to basic chemical reactions -LRB- such as combustion , for example -RRB- , is because their outer valence shell is completely filled with electrons .
