The ratio of the effective number of atoms in a unit cell of $fcc$ and $bcc$ lattices is

Which statement is correct for $Fe_3O_4$?

If all ions touching an axis passing through two opposite face-centres of unit cell are removed in $NaCl$ (rock salt) structure in which $Cl^{-}$ ions form $CCP$ and $Na^{+}$ ions occupy all octahedral voids,then the effective number of $Cl^{-}$ ions per unit cell is:

Which of the following statements is incorrect?

Predict the close-packed structure of an ionic compound $A^{+} B^{-}$ in which the radius of cation and anion are $148 \ pm$ and $195 \ pm$ respectively.

What is the coordination number of sodium in $Na_2O$?