An excess of potassium ions makes KCl crystal appear violet or lilac…

The correct answer is Option (2) → A and D only

When KCl is heated in potassium vapour, K atoms deposit on the surface and lose electrons; \( \ce{Cl-} \) ions move out to combine with the \( \ce{K+} \) ions, and the released electrons occupy the vacant anionic sites (metal excess defect).

(A) Some of the anionic sites are occupied by an unpaired electron — True. Each vacant \( \ce{Cl^{-}} \) site holds one electron.
(B) Some of the anionic sites are occupied by a pair of electrons — False. Each site holds a single, unpaired electron.
(C) There are vacancies at some anionic sites — False. The sites are not left empty; an empty vacancy alone gives no colour.
(D) F-centres are created which impart colour to the crystals — True. The electron-occupied sites are the F-centres the book describes.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Metal Excess Defect – “… The anionic sites occupied by unpaired electrons are called F-centres (from the German word Farbenzenter for colour centre). They impart yellow colour to the crystals of NaCl. The colour results by excitation of these electrons when they absorb energy from the visible light falling on the crystals. Similarly, excess of lithium makes LiCl crystals pink and excess of potassium makes KCl crystals violet (or lilac).”