Option 1: "They contain no electrons."

This statement is incorrect. All matter, including electrical insulators, contains electrons. Electrons are fundamental particles that exist within atoms and molecules.

Option 2: "Electrons do not flow easily through them."

This statement is correct. Electrical insulators are materials that have high resistance to the flow of electric current. This means that electrons, which carry electric charge, cannot move easily through insulators. The tight arrangement of atoms in the insulating material restricts the movement of electrons, preventing the flow of electric current.

Option 3: "They are crystals."

This statement is not necessarily true for all electrical insulators. While some insulating materials, like quartz, are crystalline, there are also many insulators that are not crystalline. Examples of non-crystalline insulators include glass, rubber, and plastic.

Option 4: "They have more number of electrons than the protons on their surface."

This statement is incorrect. Electrical insulators, like all matter, have an equal number of protons and electrons. This balance of positive and negative charges enables the insulating material to remain electrically neutral.

In summary, the correct statement regarding the material of electrical insulators is option 2: "