What is the relation between the number density of holes $(n_h)$ and free electrons $(n_e)$ in an intrinsic semiconductor at room temperature?

The process of adding impurities to a pure semiconductor is called

Which of the following when added as an impurity into silicon produces $n-$type semiconductor?

$A$ hole in a $P-$type semiconductor is

$A$ semiconductor has equal electron and hole concentration of $6 \times 10^8 \, m^{-3}$. On doping with a certain impurity,the electron concentration increases to $9 \times 10^{12} \, m^{-3}$. The new hole concentration is:

The most commonly used material for making transistors is