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.

Explanation

`(r_(+))/(r_(-))=sqrt(2)-1` for ideal Nacl crystal
`(r_(+))/(r_(-))=0.414 implies (r_(+))/(0.414)`
`r_(+)` =103.55 pm
Tetrahdral sites
for tetrahedral voids
0.22 `le (r_(+))/(r_(-)) lt ` 0.414
`implies(r_(+))/(r_(-))=(180)/(2.50)=0.72`
no can't slipped