Question

$A,BandC$ are three biomolecules. the results of teh tests performed on them are given below :

$\begin{array}{cccc}& \text{Molisch's Test}& \text{Barfoed Test}& \text{Biuret Test}\\ A& \text{Positive}& \text{Negative}& \text{Negative}\\ B& \text{Positive}& \text{Positive}& \text{Negative}\\ C& \text{Negative}& \text{Negative}& \text{Positive}\end{array}$

$A,BandC$ are respectively:

• A. $\text{A= Lactose, B= Fructose, C = Alanine}$
• B. $\text{A = Glucose, B= Fructose, C = Albumin}$
• C. $\text{A = Lactose, B =Glucose, C= Albumin}$
• D. $\text{A=Lactose, B= Glucose, C= Alanine}$

Answer 1

The correct option is C $\text{A = Lactose, B =Glucose, C= Albumin}$

$1.$ Molisch's test :
$\to$ It detects the presence of carbohydrate.
eg. Lactose, Glucose, Fructose

This test based on the dehydration of the carbohydrate by sulfuric acid or hydrochloric acid to produce an aldehyde, which condenses with two molecules of a phenol (usually $\alpha$-naphthol), resulting in a violet ring.

$2.$ Barfoed's test:
$\to$ It detects the presence of Monosaccharides.


$3.$ Biuret's test:
$\to$ It detects the presence of peptide bond.


Lactose - carbohydrate (Disaccharide)
Glucose - Carbohydrate (Monosaccharide)
Albumin - Protein (Peptide bonds will be present)
Alanine - Amino acid (No peptide bond).
Fructose - Carbohydrate (Monosaccharide).
Sucrose - Carbohydrate (Disaccharide).

Lactose: Only Molisch's Test
Glucose: Molisch's Test and Barfoed Test
Albumin: Only Biuret Test

So, $\text{A, B, and C}$ respectively are Lactose, Glucose and Albumin.