Question

Give the correct order of initials T (true) or F (false) for following statements:
I. In an anti-fluorite structure, anions form FCC lattice and cations occupy all tetrahedral voids.
II. If the radius of cations and anions are $0.2$ $A^o$ and $0.95$ $A^o$ respectively, then coordination number of cation in the crystal is $4$.
III An atom/ion is transferred from a lattice site to an interstitial position in Frenkel defect.
IV. Density of crystal always increases due to substitutional impurity defect.

• A. TFFF
• B. FTTF
• C. TFFT
• D. TFTF

Answer 1

The correct option is D TFTF

Frenkel defect is created when an ion leaves its appropriate site in the lattice and occupies an interstitial site. A hole or vacancy is thus, produced in the lattice.
Density of crystal may increase/decrease due to substitutional impurity defect.
If the radius of cations and anions are $0.2$ $A^o$ and $0.95$ $A^o$ respectively, then coordinate number of cation in the crystal is $3$.

$\frac{r}{R}=\frac{0.2}{0.95}=0.21$
In an anti-fluorite structure, anions form FCC lattice and cations occupy all tetrahedral voids.