Choose the answer in which the three atoms and/or ions are listed in order of increasing EXPECTED size (smallest particle listed first) assuming that the simple shell model of the atom is correct. (Neglect quantum, relativistic and other advanced considerations.)

a) Cl - < S2- < Ar
b) Ar < Cl - < S2-
c) Ar < S2- < Cl -
d) Cl - < Ar < S2-
e) S2- < Cl - < Ar

Ar < Cl - < S2-

Explanation:

All the species written above are isoelectronic. This means that they all possess the same number of electrons. All the species above possess 18 electrons, the noble gas electron configuration.

However, for isoelectronic species, the greater the atomic number of the specie, the smaller it is. This is because, greater atomic number implies that their are more protons in the nucleus exerting a greater attractive force on the electrons thereby making the specie smaller in size due to high electrostatic attraction.