Consider the following statements regard to semiconductors:
1. In n-type material, free electron concentration is nearly equal to the density of donor atoms.
2. 1 part of \[{10^8}\] donor type impurity added to Ge improves its conductivity at \[30^\circ {\rm{C}}\] by a factor of 12.
3. Phosphorus is an example of n-type impurity.
4. Conductivity of Si is more sensitive to temperature than Ge.

Which of these statements are correct?
1. 1,2 and 3 only
2. 1,3 and 4 only
3. 2 and 4 only
4. 1,2,3 and 4

Hint: A semiconductor is a solid whose conductivity is in between an insulator and a conductor. The use of semiconductors is for many purposes such as manufacturing of transistors, capacitors, integrated circuits, etc.

Complete Step by Step Answer:
Let’s understand what an n-type semiconductor is. This type of semiconductor is doped with Arsenic, Phosphorus, and antimony as an impurity. So, the flow of current is due to the flow of electrons. Therefore, the concentration of free electrons equates to the density of donor atoms. Also, we find phosphorus is an example of an n-type impurity. So, statements 1 and 3 are true.

Let’s understand what doping means. Doping means the addition of impurities to a semiconductor. This results in an increase in conductivity. One part in \[{10^6}\]to \[{10^9}\]is termed moderate doping. So, 1 part of \[{10^8}\] donor type impurity improves conductivity. Therefore, statement 2 is right.
Now, we will understand conductivity sensitivity. This defines the variation of conductivity on the basis of temperature. The Silicon possesses higher conductivity sensitivity than Ge because of its higher temperature application and smaller leakage current. Therefore, the 4^th statement is true.
Hence, option 4 is right.

Note: A semiconductor of p-type is obtained by doping impurity trivalent atoms like gallium, boron, indium, etc. The addition of impurities causes holes(vacancies of electrons) in the structure. The holes carry the charge and electrons are minority carriers.