Question

{"given":"The question asks to identify which of the given options represents an intrinsic or thermodynamic defect in a crystal solid. The options provided are Schottky defect, metal excess defect due to excess cation, metal excess defect due to anion vacancy, and metal-deficient defect.","key_observation":"The core concept is the classification of point defects in crystalline solids. Point defects are broadly divided into two categories: stoichiometric (or intrinsic/thermodynamic) defects and non-stoichiometric defects. Intrinsic defects do not disturb the stoichiometry of the solid. They are inherent to the crystal and their concentration increases with temperature. Schottky and Frenkel defects are the primary examples. Non-stoichiometric defects, on the other hand, alter the fixed ratio of cations to anions.","option_analysis":[{"label":"(A)","text":"Schottky defect","verdict":"correct","explanation":"A Schottky defect is a stoichiometric defect where an equal number of cations and anions are missing from their lattice sites to maintain electrical neutrality. Since it doesn't alter the stoichiometry and is an inherent defect, it is classified as an intrinsic or thermodynamic defect."},{"label":"(B)","text":"Metal excess defect due to excess cation","verdict":"incorrect","explanation":"This is a non-stoichiometric defect. It occurs when an extra cation occupies an interstitial site, and the charge is balanced by an electron in another interstitial site. This defect alters the stoichiometry of the crystal."},{"label":"(C)","text":"Metal excess defect due to anion vacancy","verdict":"incorrect","explanation":"This is a non-stoichiometric defect where an anion is absent from its lattice site, and the resulting void is occupied by an electron (F-center) to maintain charge neutrality. This changes the stoichiometric ratio."},{"label":"(D)","text":"Metal-deficient defect","verdict":"incorrect","explanation":"This is a non-stoichiometric defect that occurs when a cation is missing from its lattice site, and the charge is balanced by an adjacent metal ion acquiring a higher positive charge. This also alters the stoichiometry."}],"answer":"(A)","formula_steps":[]}