Select the correct statements

Options

A. For CsCl unit cell (edge - length = a) : `r_(c )+r_(a)=(sqrt(3))/(2)a`
B. For NaCl unit cell (edge - length = l), `r_(c )+r_(a)=(l)/(2)`
C. The void space in a bcc unit cell is 0.68
D. The void space % in a face centred unit cell is 26 %

Answer

A,B,C,D

Explanation

In bcc structure, `r^(+)+r^(-)=(sqrt(3))/(2)a`
Hence, for CsCl, `r_(c )+r_(a)=(sqrt(3))/(2)a`
`therefore` (A) is correct,
Since, NaCl crystallizes in fcc structure
`therefore 2r_(c )+2r_(a)=` edge length of the unit cell
Hence, `r_(c )+r_(a)=(l)/(2)`
`therefore` (B) is correct.
Since packing fraction of a bcc unit cell is 0.68
`therefore` Void space `= 1-0.68=0.32`
`therefore` (C ) is not correct.
In fcc unit cell, PF = 74%
`therefore VF = 100-74=26%`
`therefore` (D) is correct.
Hence, (A), (B) and (D) are the correct answers.
So, A : B = 4 : 4
`therefore` Formula of the compound is AB
If cation occupies alternate tetrahedral viods
Total no. of cations = 4
Total no. of anions = 4
Again A : B = 4 : 4
`therefore` Formula of the compound is AB
`therefore` (D) is correct
Hence, (A), (B), (C ) and (D) are the correct answers.