Question

Statement: There are four formula units in fluorite and antifluorite structure.
State whether the given statement is true or false.
(A) True
(B) False

Answer 1

Hint : In order to answer this question, first we will discuss whether the given statement is true or false. If the statement is true then we will discuss the whole reason or concept of the units in fluorite and antifluorite structure. And then we will also discuss the structure of fluorite and antifluorite structure.

Complete Step By Step Answer:
The given statement is true.
In the structure of fluorite and antifluorite, there are four formula units.
In fluorite structure, $C{a^{2 + }}$ ions form a fcc unit cell.
In the structure of fluorite and antifluorite, there are four formula units. $C{a^{2 + }}$ ions create the fcc unit cell in fluorite structure. All of the tetrahedral holes are occupied by F ions. Each unit cell in a fcc arrangement has four particles. Thus the number of $C{a^{2 + }}$ ions is 4. The number of particles per unit cell is equal to the number of tetrahedral voids.
${F^ - }$ ions occupy all the tetrahedral holes. Each unit cell in a fcc arrangement has four particles. Thus the number of $C{a^{2 + }}$ ​ions is 4. The number of particles per unit cell is equal to the number of tetrahedral voids. As a result, there are four ${F^ - }$ ions.
The fluorite structure is a popular motif in solid state chemistry for molecules having the formula $M{X_2}$ . The eight tetrahedral interstitial sites are occupied by $X$ ions, while the regular sites of a face-centered cubic (FCC) structure are occupied by $M$ ions. This structure is adopted by several compounds, including the ubiquitous mineral fluorite $(Ca{F_2})$ .
A crystal structure for ionic compounds of the type ${M_2}X$ that is similar to fluorite $(Ca{F_2})$ except that the anions and cations are in reversed locations, with the cations occupying the $F$ sites and the anions occupying the $C{a^{2 + }}$ sites. ${K_2}O\,and\,{K_2}S$ are two examples of antifluorite structures.
Hence, the correct option is (A) True .

Note :
The cations and anions in an anti fluorite structure are arranged in the opposite direction as they are in a fluorite structure. The structure of $L{i_2}O$ is anti-fluorite. (1) The ${O^{ - 2}}$ ions form a cubic tight packed lattice (fcc structure) in the crystal structure of $L{i_2}O$ , while the $L{i^ + }$ ions fill all of the tetrahedral spaces.