Tin is characterized by a phase transition at $13\mathrm{.}2\backslash$deg C$.$ White $($b$)$ tin is stable at

room temperature, the unit cell is body centred tetragonal with a$=0\mathrm{.}40$ nm

and c $=0\mathrm{.}34$ nm$.$ Gray $($a$)$ tin has the diamond $($or zinc blende$)$ structure with

a $=0\mathrm{.}495$ nm$.$ Calculate the change in density accompanying the phase

transformation.