1.

The face diagonal length of `f.c.c.` cubic cell is `660 sqrt(2) p m`. If the radius of the cation is `110 p m`, the radius of the anion isA. `249 p m`B. `220 p m`C. `608 p m`D. `176 p m`

Answer» Correct Answer - 2
`sqrt(2)a=660sqrt(2)p m`
so `a=660 p m`
Now if tetrahedral void is occupied by cations than
`(sqrt(3))/(4)a=(r_(+)+r_(-))`
`r_(-)((sqrt(3)xx600)/(4)-110)=110[(3)/(2)sqrt(3)-1]=1.598xx110. ` So, `(r_(+))/(r_(-))=(1)/(1.598)=(1)/(1.6)=(10)/(16)=0.625`
but `(r_(+))/(r_(-))gt0.414` so it must not be occupying tetrahedral void then
`a=2(r_(+)+r_(-))" "implies" "330=r_(+)+r_(-)`
`r_(-)=220p m`
`{(r_(+))/(r_(-))=0.5` it can occupy octahedral void `}`


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