Introduction:
An elemental solid dielectric is a material that does not contain any impurities or compounds and is made up of a single type of atom. These dielectrics have a high resistivity and are commonly used in electrical insulation applications. In this question, we are asked to identify which of the given options is not an example of an elemental solid dielectric.

Explanation:
To determine which option is not an example of an elemental solid dielectric, let's analyze each option:

a) Diamond:
Diamond is an example of an elemental solid dielectric. It is a form of carbon in which carbon atoms are arranged in a crystal lattice structure. Diamond has a high resistivity and is widely used as an electrical insulator.

b) Sulphur:
Sulphur is also an example of an elemental solid dielectric. It is a non-metallic element that exists in various forms, including a solid. Sulphur has a high resistivity and can be used as a dielectric material.

c) Silicon:
Silicon is a semiconductor material and not an elemental solid dielectric. It is a metalloid element that has properties between those of a metal and a non-metal. Silicon is widely used in electronic devices due to its semiconducting properties, but it is not considered an elemental solid dielectric.

d) Germanium:
Germanium is another semiconductor material and not an elemental solid dielectric. It is also a metalloid element and has similar properties to silicon. Germanium is commonly used in electronic devices as a semiconductor but is not classified as an elemental solid dielectric.

Conclusion:
From the given options, the material that is not an example of an elemental solid dielectric is silicon (option c). Silicon and germanium are both semiconductor materials and not considered elemental solid dielectrics. Diamond and sulphur, on the other hand, are examples of elemental solid dielectrics.