Absolute Zero Temperature and Fermi Energy Level:

At absolute zero temperature, also known as 0 Kelvin or -273.15 degrees Celsius, the temperature of a substance is at its lowest possible point. At this temperature, all molecular motion ceases, and all atoms and particles are in their lowest energy state. In solid-state physics, the behavior of electrons in a material at absolute zero is of particular interest.

The Fermi energy level, named after physicist Enrico Fermi, is a concept used to describe the energy of the highest occupied electron state at absolute zero temperature. It represents the energy level below which all the states are filled with electrons and above which all the states are empty. The Fermi energy level is often used to describe the boundary between the valence band and the conduction band in a material.

Acceptors and Energy Levels:

In semiconductors, impurities can be intentionally introduced to alter their electrical properties. Acceptor impurities are atoms or molecules that can accept an electron from the semiconductor lattice, creating a missing electron or "hole" in the crystal structure. These acceptor impurities introduce energy levels within the bandgap of the semiconductor.

Valence Band and Conduction Band:

The valence band is the highest range of energy levels in a material that is completely filled with electrons at absolute zero. It represents the energy levels occupied by valence electrons, which are responsible for the material's electrical and chemical properties.

The conduction band, on the other hand, is the range of energy levels above the valence band that is empty or partially filled with electrons at absolute zero. Electrons in the conduction band are free to move and participate in electrical conduction.

Explanation of the Correct Answer:

In the case of acceptors, when an acceptor impurity is introduced into a semiconductor, it creates an energy level just above the valence band. This energy level is called the acceptor energy level. At absolute zero temperature, all electrons in the valence band are in their lowest energy state, and there are no electrons present in the acceptor energy level.

Since the Fermi energy level represents the energy level below which all states are filled, the acceptor energy level is below the Fermi energy level. This means that at absolute zero temperature, the acceptor energy level is unoccupied, and the valence band is completely filled with electrons.

Therefore, the correct answer is option 'B' - Valence Band.