Which of the following ionic crystals exhibits Schottky defect?

Schottky defect is a type of point defect that occurs when equal numbers of cations and anions are missing from their regular lattice sites, creating vacancies. This defect is typically observed in highly ionic compounds where the cations and anions are of similar sizes and the crystal has a high coordination number.

Sodium chloride (NaCl) satisfies these conditions, as the sizes of $Na^{+}$ and $Cl^{-}$ ions are comparable, and it exhibits a Schottky defect.

In contrast, Silver chloride (AgCl), Silver iodide (AgI), and Calcium fluoride (CaF_2$) have a large difference in the sizes of their cations and anions, which leads them to exhibit Frenkel defects instead.<br><br>Answer: Sodium chloride$