The third prong on a standard electric plug provides grounding.

• A. Grounding
• B. Insulation
• C. Shielding
• D. Heating

Answer: (D)

Grounding is a safety path for fault current. The third prong connects to earth ground and to the metal parts of a device or outlet. If something goes wrong and a live wire touches the metal housing, the fault current has a low-resistance route to ground. That quick surge to earth causes the breaker to trip or a fuse to blow, reducing the risk of electric shock to anyone touching the metal parts.

Insulation surrounds and isolates conductors to prevent accidental contact, but it doesn’t provide a route to earth. Shielding protects against electromagnetic interference and isn’t the function of a household plug’s third prong. Heating is a result of resistance or normal device operation, not the purpose of the grounding prong.