The correct option is Green.
Explanation
In domestic electric circuits, wires are insulated with specific colors to ensure safety and facilitate easy identification during installation and maintenance. This color-coding system distinguishes between the live, neutral, and earth wires.
- Earth Wire: The insulation is Green (or sometimes Green with Yellow stripes). This wire is connected to the ground and serves as a critical safety measure. It provides a low-resistance path for leakage current to prevent electric shocks in case of insulation failure in metallic appliances.
- Live (Phase) Wire: The insulation is traditionally Red (or Brown in modern international standards). This wire carries the high-potential current from the power source to the appliance.
- Neutral Wire: The insulation is traditionally Black (or Blue in modern international standards). This wire completes the circuit by providing a return path for the current to the source.
Key Takeaway: The standard insulation color for the earth wire in domestic circuits is Green, which distinguishes it from the Red (Live) and Black (Neutral) wires used for power transmission.