Given below are two statements :
Statement I : Frenkel defects are vacancy as well as interstitial defects.
Statement II : Frenkel defect leads to colour in ionic solids due to presence of F-centres.
Choose the most appropriate answer for the statements from the options given below :
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Remember that Frenkel defects are "dislocation" defects where stoichiometry is maintained and density remains constant, whereas color due to F-centres is a feature of metal excess defects.
To solve this question, let's examine each statement individually, validate their truthfulness, and conclude with the appropriate answer.
Statement I: Frenkel defects are vacancy as well as interstitial defects.
The Frenkel defect is a type of point defect in crystals where an atom or ion is displaced from its lattice position and takes up a place in an interstitial site. As a result, there is a simultaneous occurrence of a vacancy (where the atom or ion was originally located) and an interstitial defect (where the atom or ion moves to).
Therefore, Statement I is true as it accurately describes the nature of Frenkel defects as involving both vacancies and interstitial defects.
Statement II: Frenkel defect leads to colour in ionic solids due to presence of F-centres.
Frenkel defects do not cause coloration in ionic solids. The coloration in ionic solids is due to the presence of F-centres (also known as color centers). An F-centre is a vacancy (absence) of an anion in the crystal lattice, coupled with an electron that occupies the space. This process is not a result of Frenkel defects.
Hence, Statement II is false, as F-centres are associated with Schottky defects rather than Frenkel defects.
After analyzing both statements, we conclude that:
Statement I is true.
Statement II is false.
Thus, the correct answer is: Statement I is true but Statement II is false.
