Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Lactose crystallization occurs instantly in labile zone
Reason (R) : At higher levels of supersaturation, crystallization occurs readily without the addition of seeding material.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

In the Metastable zone, crystallization requires seeding; in the Labile zone (high supersaturation), crystallization occurs spontaneously and instantly without seeding.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The crystallization of lactose from a supersaturated solution is described by three concentration zones: metastable, intermediate, and labile.

Step 2: Detailed Explanation:
Let us analyze both statements:

• Assertion (A): Lactose crystallization occurs instantly in labile zone: This is True. The labile zone represents a state of very high supersaturation where the solution is highly unstable.

• Reason (R): At higher levels of supersaturation, crystallization occurs readily without the addition of seeding material: This is True. In the labile zone, the concentration of lactose is so high that spontaneous nucleation occurs instantly without requiring any external seed crystals (seeding). This spontaneous nucleation triggers rapid, instant crystallization.
Since the high level of supersaturation (R) is the physical cause of spontaneous crystallization in the labile zone (A), Statement (R) is the correct explanation of (A).

Step 3: Final Answer
Both (A) and (R) are true, and (R) is the correct explanation of (A).