(3) The band gap of each germanium atomic energy level is small

the band gap of each germanium atomic energy level is small. In semiconductors like germanium, the energy gap between the valence band (with electrons) and the conduction band (with available energy states for electrons to move) is relatively small, allowing some electrons to move from the valence band to the conduction band when provided with a small amount of energy. This characteristic makes germanium a semiconductor and gives it its electrical conductivity properties in the specified range.