In the energy band diagram of a material shown in the figure,the open circles and filled circles denote holes and electrons,respectively. The material is:

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:

Which statement is correct regarding the charge of doped semiconductors?

The most commonly used material for making transistors is

If $n_e$ and $v_d$ are the number of electrons and drift velocity in a semiconductor, respectively, what happens when the temperature is increased?

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?