Through a semiconductor,an electric current is due to the drift of

Statement-$I$: By doping silicon semiconductor with pentavalent material,the electron density increases.
Statement-$II$: The $n$-type semiconductor has a net negative charge.
In the light of the above statements,choose the most appropriate answer from the options given below:

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

When an $N-$type semiconductor is heated,what happens to the charge carriers?

Which of the following statements is true?

The valence of the impurity atom that is to be added to a germanium crystal to make it an $N$-type semiconductor is: