$A$ piece of copper and another of germanium are cooled from room temperature to $80\, K$. The resistance of :-

In semiconductors at room temperature,

When the temperature of a semiconductor is increased,its resistance and electric conductivity respectively.

Read the following statements carefully:
$Y:$ The resistivity of a semiconductor decreases with an increase in temperature.
$Z:$ In a conducting solid,the rate of collision between free electrons and ions increases with an increase in temperature.
Select the correct statement from the following:

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:

What is the band gap energy for Germanium $(Ge)$?