Carbon, silicon and germanium atoms have four valence electrons each. and conduction bands are separated by energy band gaps represented by ${\left(E_{\mathrm{g}}\right)}_{\mathrm{C}}$ ${\left(E_{\mathrm{g}}\right)}_{\mathrm{Si}}\text{ and }{\left(E_{\mathrm{g}}\right)}_{\mathrm{Ge}}$ respectively. Which one of the following relationships is true in their case ?