When a small amount of impurity atoms are added to a semiconductor,then generally its resistivity:

The concentration of electrons in an intrinsic semiconductor is $6 \times 10^{15} \,m^{-3}$. On doping with an impurity, the electron concentration increases to $4 \times 10^{22} \,m^{-3}$. In thermal equilibrium, the concentration of the holes in the doped semiconductor is:

The number of silicon atoms per $m^3$ is $5 \times 10^{28}$. This is doped with $4.5 \times 10^{21}$ atoms $/ m^3$ of Arsenic. The ratio of the number of electrons to the number of holes after doping is (Take $n_i = 1.5 \times 10^{16} / m^3$)

What is the valency of donor impurity? Name these impurities.

$N-$ type semiconductors are obtained when germanium is doped with:

Consider an $n$-type semiconductor in which $n_e$ and $n_h$ are the number of electrons and holes,respectively.
$(A)$ Holes are minority carriers.
$(B)$ The dopant is a pentavalent atom.
$(C)$ $n_e n_h \neq n_i^2$ (where $n_i$ is the number of electrons or holes in the semiconductor when it is in its intrinsic form).
$(D)$ $n_e n_h \geq n_i^2$.
$(E)$ The holes are not generated due to the donors.
Choose the correct answer from the options given below.