$NaCl$ is heated in an atmosphere of sodium vapour. The resultant yellow colour is due to the formation of

The defect produced due to the presence of extra cations at interstitial sites is called

Which type of crystal defect is observed in the diagram given below?
$Na^{+} Cl^{-} Na^{+} Cl^{-} Na^{+} Cl^{-}$
$Cl^{-} \square Cl^{-} Na^{+} \square Na^{+}$
$Na^{+} Cl^{-} \square Cl^{-} Na^{+} Cl^{-}$
$Cl^{-} Na^{+} Cl^{-} Na^{+} \square Na^{+}$

In the Schottky defect,

In spite of long-range order in the arrangement of particles,why are the crystals usually not perfect?

Point defects are present in