Answer:
The correct answer is - the outermost shell of these elements are because their outermost shell of electrons is full (valency).
Step-by-step explanation:
The noble gases are the chemical elements that are inert, or unreactive with any other chemicals. Elements tries to complete to the outer shell by gaining, sharing, or loosing the electron.
This is the reason the that cause the inertness of the noble gases and does not takes part in the reaction, The noble gases have complete outer shell so their is no need to share, gain or loose to stable the element.
Thus, the correct answer is - the outermost shell of these elements are because their outermost shell of electrons is full (valency).