Question

10. If radius of a metal atom (A) is 5 pm and radius of an electronegative atom (B) is 20 pm, then in the unit cell

(1) A in octahedral voids, B in FCC unit

(2) A in FCC unit, B in tetrahedral void

(3) A in BCC unit, B in cubic void

(4) A in tetrahedral void, B in FCC unit

Answer 1

Hey dear,

● Answer -
(4) A in tetrahedral void, B in FCC unit

● Explanation -
# Given-
r+ = 5 pm
r- = 20 pm

# Solution -
Ratio of radii -
r+/r- = 5/20
r+/r- = 0.25

For 0.225 < r+/r- < 0.414, CN = 12 & structure of crystal is FCC.

Therefore, B being anion takes FCC places while A being a cation fills tetrahedral voids.

Hope this helps...