Insulator Identification in Electric Circuits

The question asks to identify a good electrical insulator from the given options. An electrical insulator is a material that resists the flow of electric current. Conversely, an electrical conductor allows current to flow easily.

Material Properties Analysis

• Plastic: Plastic is a polymer and typically has tightly bound electrons that cannot move freely. This property makes it an excellent electrical insulator, commonly used in wire coatings and casings.
• Graphite: Graphite is an allotrope of carbon. It contains delocalized electrons that can move freely, making it a good electrical conductor.
• Iron rod: Iron is a metal. Metals possess free electrons that readily conduct electricity. Therefore, an iron rod is a conductor.
• Mercury: Mercury is a unique metal that is liquid at room temperature. Like other metals, it has free electrons and acts as an electrical conductor.

Conclusion on Insulation

Based on the properties, plastic is the only material among the options that effectively prevents the flow of electric current. Therefore, plastic acts as a good insulator in electric circuits.