Question

Match List-I with List-II

List-I (Method) & List-II (Estimation)
(A) Kjeldahl method & (I) Estimation of Soil moisture
(B) Walkley & Black method & (II) Estimation of Sedimentation of soil particles
(C) Hydrometer method & (III) Estimation of Organic Carbon
(D) Gravimetric method & (IV) Estimation of Nitrogen

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

Hint:

The Kjeldahl method remains the universal standard for nitrogen analysis, while the Walkley-Black method is highly favored for soil organic carbon testing due to its simplicity and rapid execution.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Standard laboratory methods in soil science are used to analyze soil physical, chemical, and biological properties.

Step 3: Detailed Explanation:
Let us match each laboratory method with its correct application:
- (A) Kjeldahl method: This wet digestion method is the standard laboratory technique used to estimate total Nitrogen in soil and organic matter. It involves digesting organic nitrogen with sulfuric acid to form ammonium sulfate, followed by distillation and titration. Thus, (A) matches with (IV).
- (B) Walkley & Black method: This is a wet oxidation method used to estimate Organic Carbon in soil. It uses potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$) and concentrated sulfuric acid to oxidize organic carbon, followed by back-titration with ferrous ammonium sulfate. Thus, (B) matches with (III).
- (C) Hydrometer method: This is a sedimentation-based method used for soil mechanical analysis (estimating soil particle size distribution/texture). It is based on Stokes' Law, which states that larger particles settle faster in a liquid suspension than smaller particles. Thus, (C) matches with (II).
- (D) Gravimetric method: This is the direct, standard method used to estimate soil moisture content by weighing a fresh soil sample, drying it in an oven at $105^\circ\text{C}$ to constant weight, and reweighing it. Thus, (D) matches with (I).
Combining these matches gives: (A) - (IV), (B) - (III), (C) - (II), (D) - (I).

Step 4: Final Answer:
The correct matching sequence corresponds to option (C).