Electrical conductivity of insulators is

The resistivity of a semiconductor depends upon

In semiconductors at room temperature,which of the following statements is correct regarding their energy bands?

Explain with a diagram how current flows due to electrons and holes in a pure semiconductor.

The energy of a photon of sodium light $(\lambda = 589 nm)$ is equal to the band gap of a semiconductor material. Find the value of $E/kT$ at $300 K$.

Carbon,Silicon,and Germanium have four valence electrons each. These are characterized by valence and conduction bands separated by energy band gaps respectively equal to $(E_g)_C, (E_g)_{Si},$ and $(E_g)_{Ge}$. Which of the following statements is true?