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 :

A diatomic molecule X₂ has a body-centred cubic (bcc) structure with a cell edge of 300 pm. The density of the molecule is 6.17 g cm^–3. The number of molecules present in 200 g of X₂ is :
(Avogadro constant (N _A) = 6 $$ \times $$ 10²³ mol^–1 )

'X' melts at low temperature and is a bad conductor of electricity in both liquid and solid state. X is :

Which of the following compounds is likely to show both Frenkel and Schottky defects in its crystalline form?