Bonding in a germanium crystal (semiconductor) is:

This question has Statement $1$ and Statement $2$. Of the four choices given after the Statements,choose the one that best describes the two Statements.
Statement $1$ : $A$ pure semiconductor has a negative temperature coefficient of resistance.
Statement $2$ : On raising the temperature,more charge carriers are released into the conduction band.

For a crystal system where $a = b = c$ and $\alpha = \beta = \gamma \neq 90^\circ$,the system is:

Classify solid substances based on electrical conductivity and resistivity.

GaAs is

On the basis of which principle are the band diagrams of solids classified into different types?