Which of the following metals, shown by its chemical symbol, is generally used for making the filament of an electric bulb?

Introduction / Context:
Electric bulbs produce light when an electric current passes through a filament and heats it to a very high temperature. The material of the filament must withstand high temperatures without melting and must have suitable electrical and mechanical properties. General science exams often ask which metal is used for this purpose, usually presenting the answer in terms of its chemical symbol. This connects everyday technology to basic chemistry.

Given Data / Assumptions:

• The options are Fe (iron), Sn (tin), Ag (silver), and W (tungsten).
• The question is specifically about filaments of incandescent electric bulbs.
• We assume standard incandescent bulb design, not modern LED lamps.

Concept / Approach:
The ideal filament material must have a very high melting point, good tensile strength at high temperatures, and an acceptable electrical resistance. Tungsten, with the chemical symbol W, meets these requirements. It has one of the highest melting points of any metal and can glow white hot without melting inside the bulb when protected from oxygen. Iron, tin, and silver melt at much lower temperatures and would fail quickly in a bulb filament.

Step-by-Step Solution:
1. Recall that traditional incandescent bulbs use a filament that becomes white hot when electric current flows through it.2. Tungsten has a melting point of over 3400 degrees Celsius, which allows it to operate safely at the high temperatures needed for visible light emission.3. The chemical symbol for tungsten is W, derived from its old name wolfram.4. Iron (Fe) melts at a significantly lower temperature and would oxidise or melt in normal bulb operating conditions.5. Tin (Sn) and silver (Ag) also have relatively low melting points and poor performance as high temperature filaments.6. Therefore, the correct symbol for the filament metal is W for tungsten.

Verification / Alternative check:
Physics and general science textbooks state that the filament of an ordinary electric bulb is made of tungsten. Diagrams of bulb construction label the filament as tungsten and sometimes mention the symbol W. Historical developments in lighting technology note that earlier materials such as carbon were replaced by tungsten because of its superior high temperature properties. Modern halogen lamps also use tungsten filaments in a halogen gas environment to extend filament life.

Why Other Options Are Wrong:
Option A, Fe, represents iron, which rusts easily and has a lower melting point, making it unsuitable for glowing filaments. Option B, Sn, is tin, a soft metal with a low melting point often used for solder, not for high temperature filaments. Option C, Ag, is silver, an excellent conductor but not ideal as a filament because it melts at lower temperatures and would evaporate or break quickly. Only W corresponds to tungsten, the actual filament material.

Common Pitfalls:
Students sometimes confuse electrical conductors used in wiring, such as copper and silver, with filament materials, forgetting that high temperature resistance is more important in filaments. Another pitfall is unfamiliarity with the symbol W for tungsten, since the letter does not appear in the English name. To avoid mistakes, remember the special case that tungsten is W and is used for bulb filaments because of its very high melting point.

Final Answer:
The metal used for making the filament of an electric bulb is tungsten, whose chemical symbol is W.