Select the right expression for determining the Packing fraction (PF) of NaCl unit cell (assume an ideal crystal), if the ions along an edge diagonal are absent: (Where r+ represents the radius of the cation and r− represents the radius of the anion)

Select the right expression for determining the Packing fraction (PF)

1.	Select the right expression for determining the Packing fraction (PF) of NaCl unit cell (assume an ideal crystal), if the ions along an edge diagonal are absent: (Where r+ represents the radius of the cation and r− represents the radius of the anion)
Answer» Select the right expression for determining the Packing fraction (PF) of NaCl unit cell (assume an ideal crystal), if the ions along an edge diagonal are absent: (Where $r_{+}$ represents the radius of the cation and $r_{-}$ represents the radius of the anion)