Question

Molisch test is used for the detection of:
(A) Fats
(B) Carbohydrates
(C) Alkyl halide
(D) Alkaloid

Answer 1

The correct answer to this question is the very important dietary sourIt It provides energy for day-to-day activities. It is the most common form of sugars, fibers, and starch. It is a macronutrient and chemically it is made up of carbon, hydrogen, and oxygen.

Complete answer:
Molisch test is a chemical qualitative test to identify the presence of carbohydrates in any given sample. It is named after ‘Hans Molisch’ who is an Austrian botanist. This test gives a positive result for all types of carbohydrates whether it is a mono, di, or polysaccharide or is present in free form or combined form. There is an exception that tetroses and trioses do not show a positive result for molisch reagent.
In the Molisch test there is the addition of molisch’s reagent to the given sample and then subsequent addition of a few drops of sulphuric acid ${H_2}S{O_4}$ in the mixture. Molisch’s reagent is a solution containing alpha-naphthol in ethanol. The final result is that there is a formation of a purplish-red or a purple ring at the point of contact between the ${H_2}S{O_4}$ and the mixture of samples along with Molisch’s reagent. This result confirms the presence of carbohydrates in the given sample.
The basic principle behind the Molisch test is that in the sample if carbohydrate is present then on the addition of concentrated $HCl$ or ${H_2}S{O_4}$ it will undergo dehydration to form an aldehyde. Then this aldehyde will undergo condensation with two phenol-type molecules, resulting in the formation of the purple or purplish-red colored complex.
Therefore the correct option for the above question is B. carbohydrates.

Note:
While performing the Molisch’s test correct procedure needs to be followed. And necessary precautions need to be taken while following the procedure. One needs to make sure that while adding acid (concentrated $HCl$ or ${H_2}S{O_4}$ ) you should add it drop-wise along the walls of the test tube so that formation of the layer is possible and there is no mixing taking place.