Answer:

In the given options, the element that is not a semiconductor is option 'C', which is carbon (C).

Explanation:

To understand why carbon is not a semiconductor, it is important to know the basic properties of semiconductors and the electronic configuration of the 14th group elements.

Properties of Semiconductors:
1. Semiconductors have a conductivity between that of conductors and insulators.
2. The conductivity of semiconductors can be controlled by adding impurities or by applying an electric field.
3. Semiconductors have a band gap between the valence band and the conduction band.

Electronic Configuration of Group 14 Elements:
1. Group 14 elements include carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).
2. Group 14 elements have four valence electrons in their outermost shell.

Explanation for Option 'A' (Ge):
1. Germanium (Ge) is a semiconductor.
2. It has a band gap of 0.67 eV, which allows it to behave as a semiconductor.
3. Germanium is widely used in electronic devices such as transistors and diodes.

Explanation for Option 'B' (Si):
1. Silicon (Si) is also a semiconductor.
2. It has a band gap of 1.1 eV, which enables it to exhibit semiconductor properties.
3. Silicon is one of the most commonly used materials in the semiconductor industry.

Explanation for Option 'C' (C):
1. Carbon (C) is not a semiconductor.
2. It is an insulator in its pure form, with a large band gap of 5.5 eV.
3. Carbon can exist in different forms, including diamond and graphite, which have different properties.
4. While diamond is an insulator, graphite is a conductor due to its unique layered structure.

Conclusion:
In conclusion, among the given options, carbon (C) is not a semiconductor. It is an insulator with a large band gap. Germanium (Ge) and silicon (Si) are both semiconductors commonly used in electronic devices.