Which of the following configurations represents a noble gas?
(A) $1{s^2}2{s^2}2{p^2}3{s^2}3{P^6}3{d^{10}}4{s^2}4{P^6}4{d^{10}}5{s^2}$
(B) $1{s^2}2{s^2}2{p^2}3{s^2}3{P^6}3{d^{10}}4{s^2}4{f^{14}}5{s^2}$
(C) $1{s^2}2{s^2}2{p^2}3{s^2}3{P^6}3{d^{10}}4{s^2}4{P^6}4{d^{10}}4{s^2}4{p^6}4{d^{10}}5{s^2}5{P^6}$
(D) $1{s^2}2{s^2}2{p^2}3{s^2}3{P^6}3{d^{10}}4{s^2}4{P^6}4{d^{10}}5{s^2}5{p^3}$

Hint: Elements in the same vertical column or group have similar valence shell electronic configuration the same number of electrons in the outer orbital and similar properties.

Complete answer:
All the orbitals in the valence shell of the noble gases are completely filled by electrons and it is very difficult to alter these stable arrangements by the addition or removal of electrons.
The noble gases thus exhibit very low chemical reactivity. Proceeding the noble gas family are two chemically important groups of non-metals. They are the halogens.
  Helium$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;He\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2} \\$
  Neon$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Ne\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2}2{s^2}2{p^6} \\$
  Argon$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Ar\,\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6} \\$
  Krypton$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Kr\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}4{s^2} \\$
  Xenon$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Xe\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}4{d^{10}}5{s^2}5{p^6} \\$
  Radon$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Rn\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}4{d^{10}}5{s^2}5{p^6}4{f^{14}}5{d^{10}}6{s^2}6{p^6} \\ $
The correct answer is (C).

Additional Information: Atomic radius to refer to both covalent or metallic radius depending on whether the element is a metal or not. It can be measured by X-ray or other spectroscopic methods.
The atomic size generally decreases across a period, for the elements of the second period. This is because within a period the other electrons are in the same valence shell and the effective nuclear charge increases as the atomic number increases, increasing attraction of electrons to the nucleus.

Note:
The atomic radii of noble gases are not considered here, Being monatomic, and their (non-bonded radii) values are very large.
Radii of noble gases should be compared not with the covalent radii but with the Van der Waals radii of other elements.