The correct option is Green insulation.
Explanation
In domestic electric circuits, insulation colour coding is standardized to facilitate the identification of wires and ensure safety during installation and maintenance. The three primary wires used in a typical household circuit are the Live (Phase), Neutral, and Earth wires.
Analysis of Colour Coding
- Earth Wire (Protective): This wire provides a low-resistance path for leakage current to the ground, protecting the user from electric shock. It is conventionally insulated with Green (or sometimes Green with Yellow stripes) material.
- Live Wire (Phase): This wire carries the current from the source to the appliance. By convention, it has Red (or Brown in newer standards) insulation.
- Neutral Wire: This wire completes the circuit by providing a return path for the current. It typically has Black (or Blue in newer standards) insulation.
Therefore, the green insulation is specifically designated for the earth or protective wire.
Key Takeaway: In standard domestic electric wiring, the Earth wire is Green, the Live wire is Red (or Brown), and the Neutral wire is Black (or Blue).