The vacant space in the $bcc$ unit cell is .............. $\%$

An element crystallises in a face-centred cubic (fcc) unit cell with cell edge $a$. The distance between the centres of two nearest octahedral voids in the crystal lattice is

The number of octahedral sites per sphere in a $fcc$ structure is

The coordination number of cation and anion in fluorite $CaF_2$ and anti-fluorite $Na_2O$ are respectively

Which of the following statements is incorrect?

$A$ cubic unit cell contains manganese ions at the corners and fluoride ions at the centres of each edge. The coordination number of the manganese ion is-