Question

A gas filled in electric bulb is:
(a) Argon
(b) Krypton
(c) Xenon
(d) All of these

Answer 1

Hint: A noble gas is used as a filler gas in electric bulbs along with a small amount of nitrogen. Noble gas has no tendency to react. It is because of this inertness, that noble gases find use in such application.

Complete step by step answer:
The main reason that bulbs are filled with an inert gas is to reduce evaporation of the filament and prevent its oxidation.
The most popularly used filling in electric bulbs is a mixture of Argon and Nitrogen. However, due to the lesser amount of Nitrogen (around 7 %), it is known as Argon fills. Inside a bulb, this gas (mixture) is maintained at a pressure of about 0.7 atm or 70kPa.
Argon is preferred because of its inert nature, lower conductivity and most importantly, lower cost.
Nitrogen is added to the fill, in order to increase its breakdown voltage and to prevent arcing between parts of the filament.
Therefore, the answer is – option (a) – A gas filled in electric bulbs is Argon.

Additional Information:
Other than Argon, Krypton is also used as a filler gas. But owing to its higher cost, it is not as popularly used as Argon.

Note: You might’ve noticed that electric bulbs generally turn black with time. This is due to the metal ‘tungsten’ which is used to make filaments in bulbs. The tungsten, on heating, evaporates and condenses on the inner surface of the glass bulb, hence making it dark.