Option (A) is correct.
A noble gas is different from other elements because its highest electron energy level is completely filled.The examples of noble gases are helium, neon, Argon , krypton,Xenon , radon.
All the noble gases have completely filled outermost shell. for example, Helium has two electrons and both of them are present in first shell. Neon has 10 electrons, so its electronic configuration is 2,8.It has two electrons in the first shell and eight electrons in the second shell. Thus the outermost shell of both Helium and Neon is completely filled.
This property of having completely filled outermost shells makes noble gases different from the rest of the elements.These noble gases are very less reactive .
