When germanium is doped with phosphorus,the doped material has

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:

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

If the ratio of the number density of electrons to the number density of holes in a semiconductor is $7/5$ and the ratio of their currents is $7/4$,what is the ratio of their drift velocities?

An $n$-type and a $p$-type silicon semiconductor can be obtained by doping pure silicon with

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