Sodium metal crystallises in a body centred cubic lattice with edge length of $x \mathop {\rm{A}}\limits^{\rm{o}}$. If the radius of sodium atom is $1.86 \mathop {\rm{A}}\limits^{\rm{o}}$ the value of $x$ is

The incorrect statement about crystals with schottky defect is

A metal crystallises in two cubic phases, fcc and bcc with edge lengths $3.5 \mathop {\rm{A}}\limits^{\rm{o}}$ and $3 \mathop {\rm{A}}\limits^{\rm{o}}$ respectively. The ratio of densities of fcc and bcc is approximately

A solid contains elements $A$ and $B$. Anions of $B$ form ccp lattice. Cations of $A$ occupy 50\% of octahedral voids and 50\% of tetrahedral voids. What is the molecular formula of the solid?