Doping of a semiconductor (with small impurity atoms) generally changes the resistivity as follows.

What will be the conductivity of a pure silicon crystal at $300 \ K$? Given that the intrinsic carrier concentration is $1.072 \times 10^{10} \ cm^{-3}$ and at this temperature,the electron mobility $\mu_n = 1350 \ cm^2 / (V \cdot s)$ and hole mobility $\mu_p = 480 \ cm^2 / (V \cdot s)$.

In an intrinsic semiconductor,the energy gap $E_{g}$ is $1.2 \; eV$. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at $600 \; K$ and that at $300 \; K$? Assume that the temperature dependence of intrinsic carrier concentration $n_{i}$ is given by $n_{i} = n_{0} \exp \left(-\frac{E_{g}}{2 k_{B} T}\right)$,where $n_{0}$ is a constant.

Which one of the following statements is false?

Out of the following impurities, which impurity is not a trivalent?

Indium impurity is added to a sample of $Si$ to prepare a $p$-type semiconductor. In this semiconductor,one atom of indium is added per $5 \times 10^7$ atoms of $Si$. The atomic density of the $Si$ sample is $5 \times 10^{28} \text{ atoms/m}^3$. How many acceptor atoms will be present in a $1 \text{ cm}^3$ cube of silicon?