Directions: Read the Assertion (A) and Reason (R) carefully and choose the correct alternative. Assertion (A): When common salt is kept open for a long time, it tends to absorb moisture from the air. Reason (R): Commercial common salt contains magnesium chloride, which is a deliquescent impurity.

Introduction / Context:
This Assertion and Reason question is from everyday chemistry. It focuses on why common salt sometimes becomes moist or lumpy when left exposed to air. The question highlights the role of deliquescent impurities, particularly magnesium chloride, in this behaviour. Understanding this explanation is useful for practical life and examinations testing basic properties of salts and hygroscopic substances.

Given Data / Assumptions:

• Assertion (A): Common salt absorbs moisture from the air when kept open.
• Reason (R): Common salt contains magnesium chloride.
• Pure sodium chloride by itself is not strongly deliquescent at normal conditions.
• Commercial table salt often contains small amounts of magnesium chloride and calcium chloride as impurities.

Concept / Approach:
Deliquescent substances have a strong tendency to absorb water vapour from the air and can even dissolve in the absorbed water to form a solution. Magnesium chloride and calcium chloride are examples of such substances. If common salt contains these impurities, they will attract water vapour, and the entire salt mixture may appear moist or sticky. To answer the question, we must verify both the observed property and the reason involving impurities.

Step-by-Step Solution:
Step 1: In daily life, table salt sometimes becomes damp or forms lumps if it is left uncovered in a humid atmosphere. This supports Assertion (A) and shows that the behaviour described is real. Step 2: Pure sodium chloride in its ideal form does not strongly absorb moisture to the point of deliquescence under ordinary conditions. Step 3: However, commercial common salt is rarely completely pure. It often contains small quantities of magnesium chloride and calcium chloride as natural impurities. Step 4: Magnesium chloride and calcium chloride are deliquescent substances, which means they readily absorb moisture from the air and can dissolve in the absorbed water. Step 5: When common salt containing these impurities is exposed to moist air, the impurities absorb water vapour, become wet, and spread moisture through the salt crystals, making the entire mixture appear damp. Step 6: Therefore Assertion (A) is true, Reason (R) is also true, and the presence of magnesium chloride impurity directly explains the observed moistening of common salt.

Verification / Alternative check:
Chemistry textbooks often explain lump formation in salt by pointing to deliquescent impurities like magnesium chloride. They distinguish pure sodium chloride from commercial salt and note that the latter can absorb moisture because of these extra components. This confirms that Reason (R) is the correct explanation of the Assertion and not a separate unrelated fact.

Why Other Options Are Wrong:
Options that treat either the Assertion or the Reason as false go against well documented observations and textbook explanations. Suggesting that Reason (R) does not explain Assertion (A) is also incorrect because magnesium chloride is precisely the substance that causes moisture absorption in commercial salt.

Common Pitfalls:
Students sometimes think that sodium chloride itself is strongly deliquescent and ignore the role of impurities. Another confusion is mixing up hygroscopic substances, which only absorb some moisture, with deliquescent substances, which may dissolve completely. In this context, it is the impurity that is deliquescent and makes the table salt moist.

Final Answer:
Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), so the correct option is Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).