How many free electrons do semiconductors have in the valence shell?

The correct answer is based on the fundamental properties of semiconductors, which include elements like silicon and germanium. These materials are characterized by having four electrons in their outermost or valence shell. This tetravalence allows each silicon atom to form four covalent bonds with neighboring atoms, creating a stable crystal lattice that is essential for the semiconductor's functionality.

In the context of electrical conductivity, the presence of four valence electrons means that under certain conditions (like doping with other elements), some of these electrons can become free or mobile, contributing to the conduction of electricity. This tetravalent configuration is a defining aspect of semiconductors that distinguishes them from insulators and conductors, which have different numbers of valence electrons.

Understanding this concept is crucial because it lays the foundation for how semiconductors operate in electronic devices, including how they can be manipulated to enhance their conductivity through doping processes.