Identify the type of defect in brass alloy.

In the laboratory,sodium chloride is made by burning sodium in an atmosphere of chlorine. The resulting crystal is yellow in color. The cause of this yellow color is:

The correct statement regarding defects in solids is

In a crystal,Frenkel defect is observed only when the radius ratio is......

Which of the following molecular formula and type of defect are correct for the following statement?
"In $FeO$ crystal,some $Fe^{2+}$ ions are missing and the loss of positive charge is made up by the presence of $Fe^{3+}$ ions".

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