In ionic compounds where the sizes of the cation and anion are almost similar,which defect is observed?

Schottky defect generally appears in

If molten $NaCl$ contains $SrCl_2$ as impurity,crystallization can generate

In an ionic crystal,$F$-centers are.....

Use the appropriate symbols $T$ (True) or $F$ (False) for the following statements regarding defects in solids:
$(1)$ Frenkel defect arises due to the arrangement of cations and anions with a very small difference in size.
$(2)$ Frenkel defect can be called a dislocation defect.
$(3)$ $F$-centers arise due to the migration of electrons released from metal atoms into the crystal lattice.
$(4)$ Physical properties of the crystal do not change due to Schottky defect.

Which of the following crystals exhibits both Schottky and Frenkel defects?