Question

Spectroscopy useful for gas analysis is
A. Absorption spectroscopy
B. Infra-red spectroscopy
C. Emission spectroscopy
D. Nuclear magnetic resonance spectroscopy

Answer 1

Spectroscopy refers to the study of the interaction between electromagnetic radiations and matter particles. The absorption or emission of radiation gives physical and chemical properties of the matter with which they are interacting. The spectroscopy which is used for gas analysis uses infrared electromagnetic radiations.

Complete answer:
The spectroscopy technique which utilizes the infrared region of the electromagnetic spectrum is called IR or Infra-red spectroscopy. The infrared spectroscopy gives a measure of the interaction of radiation with the matter by means of absorption, reflection, or emission. Chemical substances and functional groups in the solid, gas, or liquid state are analyzed by IR spectroscopy.
An Infrared spectrometer is used which emits infrared light. This emitted light interacts with sample matter and then based on the type of interaction a graph is obtained of infrared absorbance or transmittance. The graph represents the amount of absorption or transmittance in the longitudinal axis or Y-axis vs. wavelength or frequency on the X-axis or horizontal axis.
The gas samples for infrared spectroscopy need to be prepared in long pathlength glass cells. The glass cells are cubical containers that hold the sample. The pathlength refers to the distance that will be traveled by the infra-red radiation through the sample. The long pathlength is required to compensate for the diluteness of the gas samples.
Liquid samples and solid samples can also be used for analysis through infra-red spectroscopy.

So, the correct answer is option B.

Note: A specialized glass cell is used for gas sample analysis in IR spectroscopy. These are called White’s cells. These are used in gas samples with concentrations well below ppm. This cell is equipped with mirrors that guide the infrared light to travel from the gas. These cells are available with pathlength ranging from $0.5m$ to a hundred meters.