A solid AB has NaCl type structure. If the anion has radius of 241.5 pm, what should be the minimum radius of the cation. Can cation C+ having radius of 50 pm be fitted into the tetrahedral hole of the crystal A+ B-?

Since, solid AB has NaCl type structure, coordination number will be six. The radius ratio for coordination number six will be in the range:r+r−=[0.414−0.732]For minimum radius of cation:r+r−=0.414 ⇒ r+241.5=0.414∴ r+=99.98≈100pmRadius of tetrahedral hole = r- × 0.225 = 241.5 × 0.225 = 54.33 pm Thus, cation C+ having radius of 50 pm be fitted into the tetrahedral hole.