Although crystalline solids have short range as well as long range order in the arrangement of their constituent particles, yet crystals are not perfect. Usually, a solid consists of an aggregate of large number of small crystals. These small crystals have defects in them. This happens when crystallization process occurs at fast or moderate rate. Single crystals are formed when the process of crystallization occurs at extremely slow rate. Even these crystals are not free of defects. The defects are basically irregularities in the arrangement of constituent particles. Broadly speaking, the defects are of two types, namely, point defects and line defects. Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline substance, whereas the line defects are the irregularities or deviations from ideal arrangement in entire rows of lattice points. These irregularities are called crystal defects.

Which of the following is a type of point defects?

All of these

The correct answer is option 4. All of these.

Point defects include both stoichiometric defects and non-stoichiometric defects, as well as impurity defects.

1. Stoichiometric defects: These defects involve a deviation from the ideal stoichiometry of the compound, where the ratio of atoms or ions in the compound is altered. Examples include vacancies, interstitials, and Frenkel defects.

2. Impurity defects: These defects occur when foreign atoms or ions are present in the crystal lattice, either substituting for regular lattice sites (substitutional impurity) or occupying interstitial positions (interstitial impurity).

3. Non-stoichiometric defects: These defects also involve a deviation from the ideal stoichiometry of the compound, but they typically result from the presence of excess or deficient atoms or ions within the crystal lattice. Examples include metal excess defects and metal deficiency defects.

All of these types of defects are considered point defects because they involve deviations or irregularities at the atomic or molecular scale within the crystal lattice of a solid material.