Pure sodium $(Na)$ is a good conductor of electricity because the $3s$ and $3p$ atomic bands overlap to form a partially filled conduction band. By contrast,the ionic sodium chloride $(NaCl)$ crystal is:

The electrical conductivities of $Ge$ and $Na$ are $\sigma_1$ and $\sigma_2$ respectively. If these materials are heated,then:

Why is the motion of an electron in a solid different from that in an isolated atom?

The resistance of a semiconductor at $0 \ K$ is:

Would there be any advantage to adding $n$-type or $p$-type impurities to copper?

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.