According to the International Soil Science Society (ISSS / IUSS) particle size classification scheme:
Coarse Sand: $0.2\text{ mm} - 2.0\text{ mm}$
Fine Sand: $0.02\text{ mm} - 0.2\text{ mm}$
Silt: $0.002\text{ mm} - 0.02\text{ mm}$
Clay: $\lt 0.002\text{ mm}$

Historical evolution of the tensiometer:
Burton E. Livingston (1908) was the first plant physiologist to design porous porcelain cup atmometers and auto-irrigators operating on capillary suction principles, laying the foundational conceptual design of the tensiometer.
Later, Willard Gardner (1922) developed capillary tension potentiometers in soil physics.
Lorenzo A. Richards (1928, 1931) refined and popularized the modern field tensiometer with vacuum mercury manometers and porous ceramic cups.
Following the official NTA answer key, Option 3 (B. E. Livingston) is designated as the original pioneer.

Statement (I) is true: When pyrite ($\text{FeS}_2$) in potential acid sulfate soils is oxidized upon drainage/aeration, sulfuric acid ($\text{H}_2\text{SO}_4$) is produced, causing soil pH to plummet below 3.5 - 4.0. Under this extreme acidity, clay minerals dissolve, mobilizing toxic concentrations of dissolved aluminum ($\text{Al}^{3+}$), iron ($\text{Fe}^{2+}/\text{Fe}^{3+}$), and manganese ($\text{Mn}^{2+}$) into soil solution and adjacent drainage waterways, causing massive fish kills and ecotoxicity.
Statement (II) is false: Acid sulfate soils (often called 'cat-clays') are among the most inhospitable, infertile problem soils on Earth. Despite sometimes originating in organic-rich coastal mangrove sediments, extreme acidity causes severe acute aluminum and iron toxicities, profound phosphorus fixation, and nutrient deficiencies that prevent almost all conventional crops and diverse plant life from growing without massive reclamation (intensive liming and leaching).