Question

Match List-I with List-II

List-I (Adulterant in milk)	List-II (Reagent)
(A) Sugar	(I) Barfoed's Reagent
(B) Ammonium Salts	(II) Silver nitrate
(C) Glucose	(III) Seliwanoff's Reagent
(D) Salt	(IV) Nessler's Reagent

Choose the correct answer from the options given below

• (A) - (III), (B) - (IV), (C) - (I), (D) - (II)
• (A) - (II), (B) - (I), (C) - (IV), (D) - (III)
• (A) - (I), (B) - (II), (C) - (IV), (D) - (III)
• (A) - (IV), (B) - (III), (C) - (II), (D) - (I)

Hint:

Keep this key reagent guide in mind for milk adulterants:
- Sucrose/Sugar \(\rightarrow\) Seliwanoff's reagent (Red color).
- Ammonium salts \(\rightarrow\) Nessler's reagent (Yellow-brown precipitate).
- Glucose \(\rightarrow\) Barfoed's reagent (Rapid red precipitate).
- Added salt \(\rightarrow\) Silver nitrate (Chloride titration).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Adulterants are illegally added to milk to increase its volume, density, or solids-not-fat (SNF) content.
Specific chemical reagents are used to detect these foreign substances by producing characteristic color changes or precipitates.

Step 2: Detailed Explanation:
Let us match each milk adulterant in List-I with its specific detection reagent in List-II:
-(A) Sugar (Sucrose):
Cane sugar is added to milk to artificially increase its density and SNF reading.
As discussed in Seliwanoff's method, sucrose is hydrolyzed to fructose, which reacts with Seliwanoff's reagent (resorcinol in HCl) to produce a cherry-red color.
Therefore, (A) matches with (III).
-(B) Ammonium Salts:
Ammonium sulfate or other ammonium salts are added to milk to increase its nitrogen content, masking dilution with water during Kjeldahl protein analysis.
These salts are detected using Nessler's reagent (potassium tetraiodomercurate), which reacts with ammonium ions to form a yellow or reddish-brown precipitate.
Therefore, (B) matches with (IV).
-(C) Glucose:
Glucose is a simple reducing monosaccharide added to increase the lactometer reading of diluted milk.
It is detected using Barfoed's reagent (copper acetate in acetic acid).
Since glucose is a monosaccharide, it reduces copper ions much faster than lactose (a disaccharide), forming a red precipitate of cuprous oxide within a short heating time.
Therefore, (C) matches with (I).
-(D) Salt (Sodium Chloride):
Common salt is added to diluted milk to restore its specific gravity and refractive index.
It is detected by adding silver nitrate (\(\text{AgNO}_3\)) and potassium chromate.
The silver ions react with chloride ions to form a white silver chloride precipitate, as seen in argentometric screening.
Therefore, (D) matches with (II).
This matching sequence corresponds to Option (A).

Step 3: Final Answer:
The correct matching sequence is (A) - (III), (B) - (IV), (C) - (I), (D) - (II).