Earthing (grounding) means connecting the exposed conductive parts of an appliance — its metal body, frame or enclosure — to the general mass of earth through a low-resistance conductor. Earth is treated as a reference at essentially zero potential (0 V).

Its safety role rests on what happens during an insulation failure:

• If a live wire inside the equipment touches the metal casing (a fault), the casing would otherwise rise to a dangerous voltage. Anyone touching it would provide a path for current to flow to earth through their body, causing a potentially fatal electric shock.
• With earthing in place, the fault current instead flows through the low-resistance earth conductor, which is a far easier path than a human body. This holds the casing at (or very near) earth potential, so touching it stays safe.
• The large fault current that flows also causes the fuse or MCB to operate quickly, disconnecting the faulty equipment from the supply.

Hence the primary purpose is protection of people from electric shock, which is the correct choice.

The remaining options confuse earthing with unrelated effects. Earthing does not reduce power consumption — the earth conductor carries no current in normal healthy operation, so it neither adds to nor subtracts from energy used. It does not increase wire length in any functional sense, and it has nothing to do with the brightness of a lamp, which depends on the voltage and power delivered to the load, not on the safety earth.