Which is not the correct statement for ionic solids in which positive and negative ions are held by strong electrostatic attractive forces

a. The radius r ⁺ /  r ^–  increase as coordination number increases

b. As the difference in size of ions increases, coordination number increases

c. When coordination number is eight the r ⁺ /  r ^– ratio lies between 0.225 to 0.414

d. In ionic solid of the type AX(ZnS , Wurtzite ) the coordination number of Zn ²⁺  and Sv^2-  respectively are 4 and 4

Ans. c