Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Saline soils are dominated by neutral soluble salts consisting of chlorides and sulphates of sodium, calcium and magnesium.
Reason (R): Sodic soils contain sodium salts capable of causing alkaline hydrolysis, mainly \(\text{Na}_2\text{CO}_3\).
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:

- Saline soils = Neutral salts (\(\text{NaCl}\), \(\text{Na}_2\text{SO}_4\)), \(\text{pH} < 8.5\).
- Sodic soils = Basic hydrolyzing salts (\(\text{Na}_2\text{CO}_3\)), \(\text{pH} > 8.5\).
These are distinct classes of salt-affected soils.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Salt-affected soils are classified into saline, sodic (alkali), and saline-sodic soils based on their chemical composition, electrical conductivity (EC), and exchangeable sodium percentage (ESP).

Step 2: Detailed Explanation:
- Assertion (A) evaluation: Saline soils are characterized by an excess of neutral soluble salts (chlorides and sulfates of \(\text{Na}^+\), \(\text{Ca}^{2+}\), and \(\text{Mg}^{2+}\)). These soils have high electrical conductivity (\(\text{EC} > 4 \text{ dS/m}\)) and a pH typically below 8.5. Thus, Assertion (A) is true.
- Reason (R) evaluation: Sodic (alkali) soils are dominated by sodium salts that undergo alkaline hydrolysis (primarily sodium carbonate, \(\text{Na}_2\text{CO}_3\), and sodium bicarbonate, \(\text{NaHCO}_3\)), which raises the soil pH above 8.5 and disperses clay. Thus, Reason (R) is true.
- Explanation check: While both statements are true descriptions of saline and sodic soils, respectively, they represent two distinct soil classifications. The properties of sodic soils (R) do not explain why saline soils are dominated by neutral soluble salts (A). Therefore, (R) is not the correct explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true but (R) is NOT the correct explanation of (A). This corresponds to option (B).