Element X has an atomic radius that is smaller than that of sulfur - VCE - SSCE Chemistry - Question 14 - 2005 - Paper 1

The second criterion is that the element X must commonly form an ion that has the same electron configuration as the Sb^3+ ion. The electron configuration of the Sb^3+ ion is

$[Kr]$

which indicates that the element X should also have an electron configuration that allows it to achieve a similar filled shell structure after losing three electrons.

Now we will evaluate the options:

• A. Oxygen: Has an atomic radius smaller than sulfur and can form an ion (O²⁻) but the electron configuration will not match Sb^3+.
• B. Chlorine: Also has a smaller atomic radius than sulfur and forms Cl⁻, but again does not match Sb^3+.
• C. Argon: Has an atomic radius smaller than sulfur and has the same electron configuration as Sb^3+ when considering ionic charge.
• D. Potassium: Has a larger atomic radius than sulfur and does not qualify.

Hence, the best candidate that fulfills both criteria is C. Argon.