Given: Radius of cation (r^{+} ) = 50 pm

To find: Radius of anion (r^{−} ) = ?

Formula: Radius ratio = Radius of the cation/Radius of the anion

Calculation: ZnS has tetrahedral arrangement.

The range of r^{+}/r^{-} for stable four fold coordination is 0.225 to 0.414

Hence the radius of anion can be calculated by