Which one of the following is not a semiconductor?

A semiconductor is a substance whose electrical conductivity lies between that of a conductor and an insulator. Semiconductors conduct electricity better than insulators but not as efficiently as metals. Their conductivity increases with temperature or when doped with impurities, making them essential materials in electronic devices.

Elements such as silicon (Si), germanium (Ge), and selenium (Se) are classic examples of semiconductors. They belong to the group of elements known as metalloids, which exhibit both metallic and non-metallic properties. Silicon and germanium are the most widely used semiconductors in the electronics industry due to their stable crystal structures and predictable conductivity behavior. Selenium, in its crystalline form, also behaves as a semiconductor and finds use in photocells and light meters.

Tin (Sn), however, is a metallic element and a good conductor of electricity rather than a semiconductor. It belongs to Group 14 of the periodic table, the same group as silicon and germanium, but due to its metallic bonding and free movement of electrons, tin exhibits high electrical conductivity typical of metals. Tin does not show the controlled conductivity behavior required for semiconductors.

The ability of an element to act as a semiconductor depends on its band gap energy — the energy difference between the valence band and the conduction band. Semiconductors have small band gaps (about 0.5–2 eV), whereas metals like tin have overlapping bands, resulting in continuous electron flow.

Therefore, while silicon, germanium, and selenium are true semiconductors, tin is not. This distinction is important in understanding the electronic structure of elements and their applications in inorganic and solid-state chemistry