Question

Which of the following orders are correct regarding their covalent bond character? 
i. KF $<$ KI 
ii. SnCl2 $<$ SnCl4 
iii. NaCl $<$ CuCl

• A. i, ii, iii
• B. i, iii only
• C. ii, iii only
• D. i, ii only

Hint:

Remember that Fajans' rules can sometimes provide general trends, but exceptions may occur due to various influences like electronic configuration and oxidation states.

Answer 1

The Correct Option is A

Step 1: Analyze the molecular geometries. 
Set i: Both molecules are tetrahedral, sharing identical electron pair geometries. 
Set ii: Both molecules have a pyramidal structure, albeit $<NF_3>$ with bonding pairs and $<XeO_3>$ with lone pairs affecting the structure. 
Set iii: Both are linear, having the simplest geometric arrangement. 
Step 2: Comparison with Set iv. Set iv does not contain isostructural molecules due to the different spatial arrangements ($<SF_4>$ see-saw vs. $<XeF_4>$ square planar).