Question

A cheque was suspected to be forged. Which technique could be used to compare the various pigments in the different inks?
A. Chromatography
B. Evaporation
C. Crystallization
D. Sublimation

Answer 1

Hint: There are various separation techniques used to detect the samples. Pigment samples can be detected by their affinity to travel to various solvents they are dipped in that are based on adsorption of the ink. This technique can be done with a stationary phase (can be paper) and a mobile solvent to carry on adsorption.

Complete answer:
We have been given a situation of a forged cheque and to detect the various ink pigments. The technique that must be used in this detection is chromatography.
Chromatography is a technique that is used to separate components of a mixture based on the process of adsorption. This technique uses a stationary phase that can be a solid. The solvent used acts as a mobile phase that moves on the stationary phase and the components of the mixture get adsorbed at different levels.
So, when the ink is subjected to a mobile phase solvent it can travel to various levels giving us separated pigments of various inks.
Hence, the technique used to compare the various pigments in the different inks is chromatography.

So, option A is correct.

Note:
The level of adsorption of pigments can be determined through the retardation factor or ${{R}_{f}}$ factor. It is calculated by distance travelled by the component upon distance travelled by the solvent. This is also called the relative adsorption of the components. There are various types of chromatography like column, paper, partition, thin plate etc.