Question

The edge length of $fcc$ cell is $508pm$. If the radius of the cation is $110pm$, the radius of the anion is:

• A. 110 pm
• B. 220 pm
• C. 285 pm
• D. 144 pm

Answer 1

Answer: (D)

144 pm

For $fcc$ cell, assuming anion occupies $fcc$ structure and cation occupies octahedral voids.

${2r}_{+}+{2r}_{-}=a2\times 110+2r_{-}=508r_{-}=144pm$.