The arrangement of X− ions around A+ ion in solid AX is given in the figure (not drawn to scale). If the radius of X− is 250 pm, the radius of A+ is
104 pm
From figure,
A⊕ is present in the octahedral void of X⊖
For octahedral void,
rA⊕rX⊖=0.414
⇒rA⊕=0.414×rX⊖=0.414×250 pm≃104 pm