Question

The yellow colour in $NaCl$ crystals is due to

• A. excitation of electrons in F-centres
• B. reflection of light from $Cl^-$ ions on the surface
• C. refraction of light from $Na^+$ ions
• D. all of the above

Answer 1

Answer: (A)

excitation of electrons in F-centres

Answer 2

The yellow colour is due to metal excess defect of anionic valency. $Na ^{+}$ion deposited on the surface of crystal of $NaCl$. The $Cl ^{-}$ion diffused to form $NaCl$. This happens by loss of electron from $Na$ to $Na ^{+}$at $F$ centres.