Stoichiometric defects are also called ........................ .

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

The formula of nickel oxide with metal deficiency defect in its crystal is $Ni_{0.98}O$. The crystal contains $Ni^{2+}$ and $Ni^{3+}$ ions. The fraction of nickel existing as $Ni^{2+}$ ions in the crystal is

Calcium crystallizes in a face-centred cubic $(FCC)$ lattice with an edge length of $556 \ pm$. Calculate the density if:
$(i)$ There is $0.1 \%$ Schottky defect.
$(ii)$ There is $0.1 \%$ Frenkel defect.

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.

In spite of long-range order in the arrangement of particles,why are the crystals usually not perfect?