Final answer:
Germanium (a) is the element that is a semiconductor. When dop..ed with arsenic, it becomes an n-type semiconductor, while doplng with gallium results in a p-type semiconductor.
Step-by-step explanation:
The element that is a semiconductor is germanium (a). Semiconductors have the unique property of conducting electricity more efficiently than insulators but less efficiently than conductors. When germanium is d0ped with arsenic, it has an extra electron for conduction, making it an n-type semiconductor. Conversely, when germanium is d0ped with gallium, a hole is created for conduction, resulting in a p-type semiconductor. This is because arsenic has five valence electrons, while gallium has three, and germanium itself has four.
Similarly, silicon, another semiconductor, becomes an n-type semiconductor when d0ped with phosphorus (a) as it also has five valence electrons. When silicon is d0ped with indium (b) having three valence electrons, it becomes a p-type semiconductor.