An isolated atom of germanium has 32 electrons, arranged in subshells according to this scheme:$\mathbf{1}{\mathit{s}}^{\mathbf{2}}\mathbf{2}{\mathit{s}}^{\mathbf{2}}\mathbf{2}{\mathit{p}}^{\mathbf{6}}\mathbf{3}{\mathit{s}}^{\mathbf{2}}\mathbf{3}{\mathit{p}}^{\mathbf{6}}\mathbf{3}{\mathit{d}}^{\mathbf{10}}\mathbf{4}{\mathit{s}}^{\mathbf{2}}\mathbf{4}{\mathit{p}}^{\mathbf{2}}$ This element has the same crystal structure as silicon and, like silicon, is a semiconductor. Which of these electrons form the valence band of crystalline germanium?

An isolated atom of germanium has 32 electrons arranged in subshells: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^2$

Materials whole resistivity values lie between that of conductors and insulators are called semiconductors. Examples are silicon, germanium, etc. At room temperatures the number of free charge carriers is very less and hence they act like insulators. As we increase the temperature, the number of charge carriers that are free to move increase rapidly and hence they start behaving as conductors.

From the concept, we can get that the outermost subshells of an atom that are far from the nucleus of the atom form the valence band of an atomic structure.

Hence, according to the atomic orbital concept, there are 4 electrons in the valence band due to the contribution from subshells and that is the highest filled band.