Question

The size of the iso-electric species $C{l^ - }$, Ar and $C{a^{2 + }}$ is affected by:
a- Principal quantum number of valence shell
b- Nuclear charge
c- Azimuthal quantum number of valence shell
d- Electron-electron interaction in the outer orbitals

Answer 1

The size of the iso-electric species depends on their charges. When comparing isoelectronic series the negatively charged ions have larger size than that of the positively charged ion.

Complete answer:
Size comparison on the behalf of charge on iso-electric species:
Negative charge ion < neutral ion < positive charge ion
The reason behind this kind of observation is the nuclear charge because when negative charge is present on the atom then effective nuclear charge on the outermost electron decreases due to which the size increases. On the other hand in the case of positive charge ion the effective nuclear charge on the outermost electron increases hence, the size decreases.
Now, in the given case of the iso-electric species $C{l^ - }$, Ar and $C{a^{2 + }}$, all of the three species have a total 10 electrons.
The order of size $C{l^ - }$ > Ar > $C{a^{2 + }}$
Hence, the size of the iso-electric species $C{l^ - }$, Ar and $C{a^{2 + }}$ is affected by nuclear charge.

So, the correct option is (B) Nuclear charge.

Note: Azimuthal and principal quantum numbers are the same for all in case of iso-electronic species, so it won’t affect the size. Electron-electron interaction may cause a slight effect but it’s not a prominent reason for the size determination of isoelectronic species.