A solid `A^(o+)B^(ɵ)` has `NaCl`-type close-packed structure. If the anion has a radius of `250` pm, what should be the ideal radius for the cation? Can a cation `C^(o+)` having radius of `180` pm be slipped into the tetrahedral site of the crystal `A^(o+)B^(ɵ)`? Give reason for your answer.

Answer

103.4 pm. No

Explanation

`(r_(+)(C^+))/(r_(-)(B^-))="180pm"/"250pm"=0.72`
It does not lie in the range 0.225-0.414 . Hence, `C^+` cannot be slipped into the tetrahedral site.