A Binary solid has rocksalt structure The edge length is 400 pm and the radius of cation is 75 pm, the radius of anion is

Rock salt structure is fcc unit cell.

given that edge length, a=400pm

radius of cation, r_C​=75 pm

let radius of anion be r_A​

for fcc lattice, edge length=2r_C​+2r_A​

upon substitution we get:

400=2×75+2r_A​

2r_A​=400-150 =250

r_A  =125

radius of anion is 125$\frac{250}{2}$ pm