Question

The source that gives the line emission spectrum when subjected to dispersion is
A. Molten iron
B. Sun
C. Mercury Vapour
D. Candle

Answer 1

Hint: Light sources that are capable of primarily emitting radiation with discrete, well-defined frequencies can emit line emission spectrum when subjected to dispersion.
The early sources of spectral emission lines were simply arc lamps or some other form of electrical discharge in a sealed tube of gas in which the pressure is kept low enough so that a significant portion of the radiation is emitted in the form of discrete lines.

Complete step by step answer:
Let us examine the options one by one
Molten iron: The peak wavelength is in the infra-red region of the spectrum but quite close to the red end of visible light. Because of this the molten metal will radiate large amounts of red, orange and yellow light.

Sun: The Sun emits radiation right across the electromagnetic spectrum, from extremely high-energy X-rays to ultra-long-wavelength radio waves, and everything in-between. The peak of this emission occurs in the visible portion of the spectrum.

Mercury Vapour: A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light and when subjected to dispersion gives a line emission spectrum.

Candle: Most of flame spectrometry involves the analysis of flames produced by burning individual elements and examining their spectra. A candle wick is a combination of different materials and is constantly fueled by the wax, this produces a radiation similar to black body radiation.

The only option that fits the reasoning is mercury vapor.

So, the correct answer is “Option C”.

Note: It is helpful to know the type of radiation emitted by different light sources to solve these kinds of questions. Additionally, emission lines are usually seen as bright lines, or lines of increased intensity, on a continuous spectrum.