The filament of an electric bulb is made of

Concept: An electric bulb gives light by the heating effect of electric current — the current is driven through a thin, high-resistance wire until that wire reaches roughly 2500 °C and glows white-hot. The material of that wire is therefore fixed by three requirements: a melting point far above the working temperature, a very low rate of evaporation at that temperature so the wire does not thin out and snap, and enough ductility to be drawn into a long, fine wire that can be coiled.

Applying it here: Tungsten satisfies all three. Its melting point is about 3422 °C, some 900 °C above the working temperature, so the wire stays solid with a wide margin. Its vapour pressure at that temperature is very low, and the bulb is filled with argon or nitrogen to slow evaporation further, so a coil survives for hundreds of hours. It is also ductile enough to be drawn to a few hundredths of a millimetre and wound into a double coil, packing a long resistive length into a few millimetres.

Cross-check with the other materials:

• Iron melts at about 1538 °C, below the glow temperature itself, and scales heavily in hot air.

• Nichrome melts near 1400 °C; it is designed for the dull-red heat of a heating element, not for white heat.

• Graphite does not melt but sublimes above about 3600 °C. Carbon filaments were genuinely used in the earliest lamps from 1879, but they evaporated fast and blackened the glass, and tungsten replaced them from about 1906-1910.

Hence the filament of an electric bulb is made of tungsten.