The insulator of electricity is:
(A) Copper
(B) Silk
(C) Human body
(D) Acidulated water

Hint: We should remember that an insulator is a material which does not conduct electricity. Based on this criterion we have to classify each of the mentioned options as insulator or conductors. This will give us the answer to the required question.

Complete step by step answer:
It should be known to us that insulators are substances in which the electron does not flow freely and are tightly bound. So there is no scope for the electric charges to flow in a freeway. Moreover, with only the influence of an external electric field there will be little electric current flowing in the insulating materials.
Among the mentioned options silk is an insulator. This is because copper is a very good conductor of electricity and so is the human body. This is because of the enormous amount of free electrons present in these materials. Normal water does not conduct electricity, but when acid is added the number of free electrons increases, this makes it a conductor of electricity.

Hence the insulator of electricity is Silk. So the correct answer is Option A.

Note: We should know that the insulators are materials which possess a high resistivity and very low conductivity. The atoms are very tightly bound with the electrons that are not able to move freely throughout the substance.
The insulating materials find their application in the field of wrapping the electrical cables or any other equipment. Usually the insulators are made up of glass and porcelain.
We should also know that silk is not considered to be a great insulator. This is because when exposed to the humid atmosphere it will experience electrical conductivity.