Boron exist in different allotropic forms. All allotropic form contains icosahedral units (Icosahedral is a regular shape with 12 corners 20 faces) with boron atoms at all 12 corners and all bonds are ) equivalent.

Calculate  $\mathrm{\Delta }H\left(\mathrm{nk}J\right)$ per mole of boron atoms forming gaseous icosahedron if Ml.BE (B-B) = 200 kJ/mol: