A potassic fertiliser contains 50% K₂O. It could be

ANS:A - potassium sulphate.

Potassium sulfate, commonly known as sulfate of potash (SOP), is a chemical compound with the formula K2SO4. It is a water-soluble, white crystalline salt that contains potassium (K) and sulfate (SO4) ions. Here's an explanation of potassium sulfate and its characteristics:

1. Chemical Composition: Potassium sulfate consists of potassium ions (K+) and sulfate ions (SO4^2-) held together by ionic bonds. Each formula unit of potassium sulfate contains two potassium ions and one sulfate ion.
2. Production: Potassium sulfate can be produced by several methods, including the reaction of potassium chloride with sulfuric acid (KCl + H2SO4 → K2SO4 + HCl) or by the reaction of potassium hydroxide with sulfuric acid (2KOH + H2SO4 → K2SO4 + 2H2O). It can also be obtained as a byproduct of certain industrial processes, such as the manufacture of nitric acid or the purification of phosphate fertilizers.
3. Solubility: Potassium sulfate is highly soluble in water, which allows it to dissolve readily and be taken up by plants' root systems. Its solubility makes it suitable for use in fertigation (application through irrigation systems) and foliar spraying, providing plants with readily available potassium and sulfur nutrients.
4. Nutrient Content: Potassium sulfate is a source of both potassium (K) and sulfur (S), two essential nutrients for plant growth and development. Potassium plays a key role in regulating water uptake, enzyme activation, and overall plant metabolism. Sulfur is important for protein synthesis, chlorophyll formation, and the overall health of plants.
5. Fertilizer Use: Potassium sulfate is commonly used as a fertilizer in agriculture to supply potassium and sulfur to crops. It is particularly favored for crops that are sensitive to chloride ions, as potassium sulfate does not contain chloride, unlike potassium chloride fertilizers. Potassium sulfate is used in various crops, including fruits, vegetables, grains, and turfgrass.
6. Soil pH: Unlike some other potassium fertilizers (such as potassium hydroxide or potassium carbonate), potassium sulfate has a neutral pH, which means it does not significantly alter soil acidity or alkalinity when applied. This makes it suitable for use in soils with a wide range of pH levels.

Overall, potassium sulfate is a valuable fertilizer that provides essential nutrients to plants while avoiding potential negative effects associated with chloride-containing fertilizers. Its solubility, nutrient content, and neutral pH make it a versatile option for improving crop yields and maintaining soil fertility in agricultural systems.