Question

Which of the following is/are correct regarding defects in solids?

• A. Metal excess defect is a stoichiometric defect
• B. Stoichiometric defect is also called intrinsic defect
• C. Point defects in crystal increase thermodynamic stability
• D. All point defects result in decrease in the density of the solid

Answer 1

Answer: (B), (C)

Point defects in crystal increase thermodynamic stability

Defect is a disruption in the periodic order of a crystalline material. Point defects generally increase thermodynamic stability.

Point defect is of three types,
1. Stoichiometric defect
2. Non-Stoichiometric defect
3. Impurity defect

Point defects that do not disturb the stoichiometry of the solid are called stoichiometric defects. The tendency to show these defects depends on the temperature arrangement. These defects are also known as thermodynamic or intrinsic defects.

Non-Stoichiometric defects cause the constituent elements in solids to occur in non-stoichiometric ratios.

Metal excess defect is a non-stoichiometric defect because it will have an excess metal ion.

As density is the ratio of mass to volume, only defects where there is loss of mass of both cations and anions, show decrease in density. Others defects like Frenkel defects do not show decrease in density.
$\therefore$ Options a and c are correct.