Conductors, Insulators and Semiconductors

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

In the energy band diagram of a material shown below, the open circles and filled circles denote holes and electrons, respectively. The material is a/an 

Carbon, silicon and germanium have four valence electrons each. At room temperature, which one of following statements is most appropriate?

In an unbiased $p$ - $n$ junction, holes diffuse from the $p$ - region to $n$ - region because

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm, is incident on it. The band gap in (eV) for the semiconductor is