Question

Give reason What makes the crystal of KCl sometimes appear violet?

Answer 1

1 - it is just due to F-centre .electrons becomes xcited and when they come to the ground level they radiate energies in the visible spectrum of light thus coloura are seen .

2- The violet colour of KCl crystals is because of metal excess defect due to anionic vacancies.Excess of potassium makes KCl crystals violet or lilac.