In which of the following is an ionic bond present?

The forbidden energy gap in $Ge$ is $0.72\,eV$. Given,$hc = 12400\,eV\cdot\mathring{A}$. The maximum wavelength of radiation that will generate an electron-hole pair is..........$\mathring{A}$.

The manifestation of band structure in solids is due to

Classify solid substances based on electrical conductivity and resistivity.

Choose the correct statement. In conductors,

Which of the following substances has an energy gap $(E_g)$ greater than $3 \ eV$?