Which of the following graphs represents the temperature $(T)$ dependence of resistivity $(\rho)$ of a semiconductor?

The distance between the body-centered atom and a corner atom in sodium $(a = 4.225 \, \mathring{A})$ is ....... $\mathring{A}$ $[AIPMT \, 1995]$

For non-conductors (insulators),the energy gap is: (in $, eV$)

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

At absolute zero,$Si$ acts as

Assertion $(A)$: When a wire of aluminium and another wire of silicon are heated from room temperature to $80^{\circ} C$,the conductivity of aluminium decreases and that of silicon increases.
Reason $(R)$: Aluminium has a positive temperature coefficient of resistivity and silicon has a negative temperature coefficient of resistivity.