Question

The edge length of the face-centered cubic unit cell is 508 pm. If the radius of the cation is 110 pm, the radius of the anion will be:

(a) 144 pm
(b) 288 pm
(c) 618 pm
(d) 398 pm

Answer 1

Correct option is (a) 144 pm

For the face-centered cubic unit cell (eg: NaCl),

the edge length = 2 × distance between cation and anion

= 2 (r₊ + r_–)

2(r₊ + r_–) = 508 pm

given r₊ = 110 pm

2(110 + r_–) = 508 pm

r_– = 144 pm