Question

In gaseous discharge tube, the colour of light emitted by helium is :
(A) yellow
(B) red
(C) blue
(D) green

Answer 1

Hint: A gas discharge tube is usually a glass tube with two electrodes sealed through its walls. When a voltage is applied to the two electrodes and the pressure of the gas in the tube is reduced, eventually a pressure is reached at which a current flows, and the gas begins to glow.

Complete step by step answer:
Helium is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. Helium is the second lightest and second most abundant element in the observable universe (hydrogen is the lightest and most abundant). It is present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined.
When an electric current is passed through a gas, the gas emits light. This emission is exploited in many electric lamps. Fluorescent lamps, “neon” signs, and mercury-vapor and sodium-vapor lamps are common examples of this kind of electric lighting, called gas-discharge lamps. The colors of gas-discharge lamps vary widely depending on the identity of the gas and the construction of the lamp.
Helium gas emits a pale yellow colour when present in an electrified discharge tube. This is used in making colourful and glowing signs.
So, the correct answer is “Option A”.

Note: The identity of the gas in the tube determines the color of the glow. Neon emits a red glow, helium produces pale yellow, and argon yields blue. Mercury vapor also emits blue light, and sodium vapor emits yellow.