The incorrect statement about crystals with Schottky defect is
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Remember the key differences between Schottky and Frenkel defects:
Schottky: Equal number of cations and anions are MISSING. Density DECREASES. Occurs when ion sizes are similar (e.g., NaCl).
Frenkel: A cation is DISLOCATED from its lattice site to an interstitial site. Density remains UNCHANGED. Occurs when there is a large difference in ion sizes (e.g., AgCl).
It is due to missing of equal number of cations and anions from lattice points
On the whole crystal is electrically neutral
It is shown by ionic compounds in which cation and anion are of almost same size
Density of the crystal increases
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The Correct Option isD
Solution and Explanation
Let's analyze the characteristics of the Schottky defect.
The Schottky defect is a type of point defect in a crystal lattice.
(A) It is due to missing of equal number of cations and anions from lattice points:
This is the definition of a Schottky defect. To maintain overall electrical neutrality, when a cation leaves its lattice site, an anion must also leave its site, creating a pair of vacancies. This statement is correct.
(B) On the whole crystal is electrically neutral:
As explained above, an equal number of positive cations and negative anions are missing from the lattice. Therefore, the overall charge of the crystal remains balanced and it stays electrically neutral. This statement is correct.
(C) It is shown by ionic compounds in which cation and anion are of almost same size:
This defect is common in highly ionic compounds where the cations and anions have similar sizes (i.e., a high coordination number). This similarity in size makes it equally probable for either ion to leave the lattice. Examples include NaCl, KCl, CsCl. This statement is correct.
(D) Density of the crystal increases:
The Schottky defect involves the removal of ions from the crystal lattice, creating vacancies. Since mass is lost from the crystal while the volume remains essentially unchanged, the density of the crystal must decrease. Density = Mass/Volume. As Mass decreases, Density decreases. This statement is incorrect.
The question asks for the incorrect statement. Therefore, option (D) is the answer.
