Solids have definite mass, volume and shape. Depending upon order, they are classified as crystalline solids and amorphous solids. Crystalline solids are further classified into molecular, ionic, metallic and covalent solids. Crystalline solids are made up of constituent particles which are arranged in a regular pattern, which is depicted in the form of three dimensional array of points in spaces called lattice points. Small characteristic repeating portion of lattice is called unit cell.
Unit cells can be primitive and also centred unit cells like face centred, body centred, end centred. Solids are not perfect. There are various types of defects (i) line defect (ii) point defect. Point defects are of three types : stoichiometric, impurity and non-stoichiometric defects. Solids show magnetic properties depending upon the orientation of electron.
Based on the paragraph Answer the following :
Match List I with List II.
| LIST I | LIST II |
| A. Schottky defect | I. Irregularities from an ideal arrangement around an atom. |
| B. Dislocation defect | II. Decreases the density of the substance |
| C. Point defect | III. Frenkel defect |
| D. Vacancy defect | IV. Number of missing cations and anions are equal |
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(IV), (B)-(III), (C)-(I), (D)-(II)
A. Schottky defect — This matches IV. Number of missing cations and anions are equal. It is a vacancy defect in ionic solids; equal numbers of cations and anions are missing so that the crystal stays electrically neutral.
B. Dislocation defect — This matches III. Frenkel defect. In a Frenkel defect the smaller ion is dislocated from its normal site to an interstitial site, so it is also called a dislocation defect.
C. Point defect — This matches I. Irregularities from an ideal arrangement around an atom. Point defects are irregularities around a point or an atom in a crystalline substance (line defects run along rows of lattice points).
D. Vacancy defect — This matches II. Decreases the density of the substance. When some lattice sites are vacant, the mass falls while the volume stays the same.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.