Question

Given below are two statements:
Statement (I): Formalin is used for preservation of milk samples meant for chemical analysis.
Statement (II): Mercuric chloride is used as preservative for milk samples meant for cryoscopic analysis (test for freezing point depression).
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true
• B. Both Statement (I) and Statement (II) are false
• C. Statement (I) is true but Statement (II) is false
• D. Statement (I) is false but Statement (II) is true

Hint:

Remember that cryoscopic analysis (freezing point test) is extremely sensitive to added solutes.
Never use ionic or highly soluble chemical preservatives in milk samples meant for freezing point determinations, as they will artificially lower the freezing point and mask added water.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Preservatives are added to milk samples to prevent microbial growth and enzymatic changes during transport and storage before analysis.
However, the choice of preservative must be carefully aligned with the type of analytical test to be performed.
This is because certain chemical agents can interfere with specific physical or chemical properties of the milk.

Step 2: Detailed Explanation:
Let us evaluate both statements:
-Statement (I): "Formalin is used for preservation of milk samples meant for chemical analysis."
This statement is true.
Formalin (a 40% formaldehyde solution) is a highly effective preservative used for milk samples intended for routine chemical testing, such as fat and solids-not-fat (SNF) estimation.
It is typically added at a concentration of 0.1 mL per 100 mL of milk.
It prevents microbial spoilage without altering the fat or total solids content.
-Statement (II): "Mercuric chloride is used as preservative for milk samples meant for cryoscopic analysis..."
This statement is false.
Cryoscopic analysis measures the freezing point depression of milk to detect the addition of water.
The freezing point of milk is a colligative property that is highly sensitive to the concentration of dissolved solutes.
Adding any soluble chemical preservative, especially an ionic salt like mercuric chloride (\(\text{HgCl}_2\)), increases the solute concentration.
This results in a significant, artificial depression of the freezing point.
Therefore, preservatives are strictly avoided for samples intended for cryoscopic analysis.
If a sample must be preserved, specific non-dissociating organic compounds are used with strict correction factors, but mercuric chloride is not used for this purpose.
Thus, Statement (I) is true but Statement (II) is false.

Step 3: Final Answer:
Statement (I) is true but Statement (II) is false, which corresponds to Option (C).