Question

Non-stoichiometric KCl shows lilac colour due to

• A. Presence of excess cations in interstitial sites
• B. Presence of excess anions in interstitial sites
• C. Absence of anions at lattice sites
• D. Absence of cations at lattice sites

Hint:

F-centre is formed due to missing anion with trapped electron.

Answer 1

The Correct Option is C

Concept:
Crystal defects are responsible for colour changes in ionic solids.
Step 1:
When an anion is missing from lattice site and electron occupies its place, F-centre is formed.
Step 2:
In KCl, absence of chloride ion creates an electron trapped in the lattice.
Step 3:
These trapped electrons absorb visible light and produce lilac colour.
Step 4:
Thus colour is due to: \[ \boxed{\text{Absence of anions at lattice sites}} \] \[ \boxed{\text{Correct Option = (3)}} \]