In everyday electric bulbs used for lighting, the thin filament that glows white hot is commonly made from which one of the following materials?

Introduction / Context:
Incandescent electric bulbs are among the oldest artificial lighting devices. This question checks whether you remember the standard material used for the glowing filament, which must withstand very high temperatures without melting and should emit visible light efficiently.

Given Data / Assumptions:
• We are talking about a conventional incandescent bulb, not LED or fluorescent lamps.
• The filament is a thin wire coil sealed in a glass bulb filled with inert gas.
• The material must have a very high melting point and suitable electrical resistance.

Concept / Approach:
The filament material must tolerate temperatures of about 2500 to 3000 degrees Celsius, radiate visible light, and have low evaporation at those temperatures. Tungsten has an extremely high melting point, high tensile strength at high temperature and relatively low evaporation rate, so it is ideal. Other metals like copper or iron would melt or evaporate too quickly at the required operating temperature. Nichrome and graphite have uses in heaters or electrodes but not as standard incandescent filaments in household bulbs.

Step-by-Step Solution:
Step 1: Recall that the filament in an incandescent bulb operates at a very high temperature to emit visible light due to incandescence. Step 2: Note that tungsten has a melting point above 3400 degrees Celsius, which is higher than most common metals. Step 3: Compare alternative materials. Copper and iron melt at much lower temperatures and would fail in normal bulb conditions. Step 4: Nichrome is used in heating elements, but it does not emit as efficient visible light as tungsten when used as a filament in a small bulb. Step 5: Therefore, the correct choice for the filament material is tungsten.

Verification / Alternative check:
If you look at technical specifications of incandescent bulbs or science textbooks, you will consistently see the phrase tungsten filament. Many exam questions specifically mention tungsten as a key example of a metal with a high melting point used for lamp filaments, which confirms this choice.

Why Other Options Are Wrong:
Nichrome: Commonly used in electric heaters and toasters, but not in standard bulb filaments because its light output is not as efficient for illumination.
Graphite: Used as an electrode material and in older arc lamps, but not in modern incandescent bulbs; it is also brittle in thin wire form.
Iron: Melts at much lower temperature and would oxidise and fail rapidly in a bulb environment.
Copper: Excellent conductor but low resistance and lower melting point, so it cannot serve as a hot, glowing filament in air or inert gas at such high temperatures.

Common Pitfalls:
A frequent mistake is to confuse heating element materials like nichrome with filament materials. Another confusion arises when students think that good conductors like copper are best for all electrical uses, forgetting that in a filament some resistance and very high temperature tolerance are actually required.

Final Answer:
The filament of a conventional electric bulb is made of Tungsten wire.