Question

Match List-I with List-II
List-I (Preservative) & List-II (Reagent used in the Test)
(A) Boric Acid & (I) Stannous chloride
(B) Formaldehyde & (II) Paraphenylenediamine
(C) Hydrogen Peroxide & (III) Ferric chloride
(D) Hypochlorite & (IV) Turmeric Paper

Choose the correct answer from the options given below:

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

Hint:

To remember key preservative tests:
- Boric Acid $\rightarrow$ Turmeric Paper (red-brown color change).
- Formaldehyde $\rightarrow$ Ferric Chloride (Hehner's purple ring).
- \(\text{H}_2\text{O}_2\) $\rightarrow$ Paraphenylenediamine (peroxidase-driven blue color).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Chemical preservatives are sometimes added illegally to milk to extend its shelf-life by inhibiting bacterial growth.
National food safety standards prescribe specific qualitative chemical tests using selective reagents to detect these adulterants.

Step 2: Detailed Explanation:
Let us analyze the chemical tests used to detect each preservative in List-I and match them with the reagents in List-II:
1. Boric Acid matches with Turmeric Paper (IV):
Boric acid (\(\text{H}_3\text{BO}_3\)) or borates react with curcumin, the active coloring agent in turmeric.
When turmeric paper is dipped in a milk sample acidified with hydrochloric acid containing boric acid, then dried, it turns a characteristic cherry-red color.
Applying a drop of ammonium hydroxide turns this red color to a dark greenish-blue, which is a specific confirmatory test for boric acid.
2. Formaldehyde matches with Ferric chloride (III):
Formaldehyde is commonly detected using Hehner's test.
In this test, the milk sample is layered over concentrated sulfuric acid containing trace amounts of ferric chloride (\(\text{FeCl}_3\)).
The ferric chloride acts as an oxidizing agent.
In the presence of formaldehyde, a distinct violet or purple ring forms at the junction of the two liquids.
3. Hydrogen Peroxide matches with Paraphenylenediamine (II):
Hydrogen peroxide (\(\text{H}_2\text{O}_2\)) is detected using the paraphenylenediamine test.
When a few drops of a paraphenylenediamine solution are added to milk containing hydrogen peroxide, the milk's native peroxidase enzyme catalyzes the oxidation of paraphenylenediamine, producing a deep blue color.
4. Hypochlorite matches with Stannous chloride (I):
Hypochlorites or chlorine-based sanitizers in milk can be detected using stannous chloride (\(\text{SnCl}_2\)).
The stannous chloride acts as a reducing agent in a starch-iodide system, where the free chlorine oxidizes iodide to iodine, forming a blue starch-iodine complex.
This matches the sequence: (A)-(IV), (B)-(III), (C)-(II), (D)-(I).

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