The N/S ratio is a critical indicator of nutritional balance in plants. Legumes generally exhibit a wider N/S ratio compared to other crops because they have a high demand for both nitrogen, which they often fix symbiotically, and sulphur, which is essential for the synthesis of sulphur-containing amino acids and proteins. Maintaining this ratio is vital for optimizing nodulation and overall yield in leguminous crops.

Necrosis, the localized death of plant tissue, is a common physiological response to the deficiency of essential macronutrients like K, P, Ca, and Mg. When these nutrients are unavailable, the plant cannot maintain cellular integrity or metabolic functions, leading to tissue breakdown. While specific patterns of necrosis (such as marginal or interveinal) can help distinguish between nutrient deficiencies, the general appearance of necrotic lesions is a hallmark symptom of severe nutrient stress in plants.

Oligotrophic water bodies are defined by their low levels of nutrients, such as phosphorus and nitrogen. This limitation restricts the growth of algae and other aquatic plants, resulting in high water transparency and low biological activity compared to eutrophic systems, which are nutrient-rich and highly productive.

The availability of manganese (Mn2+) in soil is highly dependent on pH levels. As the soil pH increases, the solubility of manganese decreases significantly due to chemical precipitation and oxidation processes. Scientific studies on soil chemistry indicate that for every single unit increase in soil pH, the concentration of available Mn2+ ions in the soil solution decreases by approximately 100-fold, which can lead to manganese deficiency in plants grown in alkaline soils.

Citric acid is a naturally occurring organic acid that acts as a chelating agent. Natural chelates are small molecules capable of penetrating plant barriers like cuticles and cell membranes, which enhances nutrient absorption. In agricultural and industrial applications, citric acid is frequently used to sequester free iron cations, thereby preventing the precipitation of iron hydroxides or sulfides in various solutions.

Soil pollution has multifaceted negative impacts. It leads to the contamination of water bodies through runoff, harming aquatic ecosystems. It poses significant food safety risks as pollutants can be absorbed by crops and enter the human or animal food chain. Furthermore, it degrades soil structure and fertility, rendering land unproductive for agricultural use.

Plant nutrition science identifies 17 essential elements required for normal plant growth, including macronutrients like Nitrogen, Phosphorus, and Potassium, and micronutrients like Zinc. While Carbon is a fundamental building block of plant biomass, it is obtained from atmospheric carbon dioxide through photosynthesis rather than being applied as a soil-based fertilizer nutrient. Therefore, in the context of agricultural fertilization, Carbon is not categorized as a fertilizer nutrient.

Single Super Phosphate (SSP) is produced by the acidulation of naturally occurring rock phosphate with sulfuric acid. This chemical reaction converts insoluble tricalcium phosphate into monocalcium phosphate, which is water-soluble and readily available for plant uptake. Historically, SSP was the first commercial mineral fertilizer, marking a significant milestone in the development of the global plant nutrient industry.

The nitrogen content of these fertilizers is as follows: Sodium nitrate (Chile saltpeter) contains approximately 16% nitrogen. Calcium nitrate contains about 15% nitrogen. Potassium nitrate contains approximately 13% nitrogen. Urea is the most concentrated solid nitrogen fertilizer, containing 46% nitrogen. Matching these values to the provided options confirms that option D is the correct pairing for the specified fertilizers and their nitrogen percentages.

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The process of lithification involves the compaction of these fine particles under pressure, resulting in the characteristic fissile structure of shale.