The Correct Answer is Option (D)

Van der Waal's bonding is attributed to the attractive forces between molecules of a liquid. The conductivity of semiconductors (covalent bonding) and insulators (ionic bonding) increases with increase in temperature while that of metals (metallic bonding) decreases.

The Correct Answer is Option (C)

A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice. The spacing between unit cells in various directions is called its lattice parameters or constants. Increasing these lattice constants will increase or widen the band-gap $\left(Eg\right)$, which means more energy would be required by electrons to reach the conduction band from the valence band. automatically $E_c$ and $E_v$ decreases.

The Correct Answer is Option (D)

Band gap $=$ energy of photon of wavelength $2480$ $nm.$ So,

$\mathrm{\Delta }E=\frac{hc}{\lambda }$

$=\left(\frac{6.63\times {10}^{-34}\times 3\times {10}^8}{2480\times {10}^{-9}}\right)\times \frac{1}{1.6\times {10}^{-19}}eV$

$=0.5eV$

The Correct Answer is Option (D)

Copper is a conductor, so its resistance decreases on decreasing temperature as thermal agitation decreases; whereas germanium is semiconductor therefore on decreasing temperature resistance increases.

The Correct Answer is Option (B)

Pauli's exclusion principle.

The Correct Answer is Option (C)

The resistance of metal (like $Cu$) decreases with decrease in temperature whereas the resistance of a semi-conductor (like $Ge$) increases with decrease in temperature.

The Correct Answer is Option (C)

Pure silicon, at absolute zero, will contain all the electrons in bounded state. The conduction band will be empty. So there will be no free electrons (in conduction band) and holes (in valence band) due to thermal agitation. Pure silicon will act as insulator.

The Correct Answer is Option (C)

Specific resistance is resistivity which is given by

$\rho =\frac{m}{m{e}^2\tau }$

where $n=no.$ of free electrons per unit volume and $\tau$ $=$ average relaxation time

For a conductor with rise in temperature $n$ increases and $\tau$ decreases. But decrease in $\tau$ is more dominant than increase in $n$ resulting an increase in the value of $\rho$

For a semiconductor with rise in temperature, $n$ increases and $\tau$ decreases. But the increase in $n$ is more dominant than decrease in $\tau$ resulting in decrease in the value of $\rho .$

The Correct Answer is Option (C)

The energy band gap is maximum in insulators.