Which of the following is an example of a decomposition reaction? MCQ with Answer and Explanation

Explanation:
NPK stands for Nitrogen (N), Phosphorus (P, as P₂O₅), and Potassium (K, as K₂O). These are primary macronutrients essential for plant growth. The numbers on a fertiliser bag (e.g., 10-26-26) indicate the percentage of N, P₂O₅, and K₂O.

Explanation:
Smelting involves heating the concentrated ore (often after roasting/calcination) with a reducing agent (like coke, CO) to reduce the metal oxide to the metal. For example, iron ore is smelted in a blast furnace. Roasting heats sulfide ores in air; calcination heats carbonate ores in absence of air; leaching dissolves out the metal.

Explanation:
Urea (CO(NH₂)₂) is a nitrogenous fertilizer with the highest nitrogen content (about 46%). Superphosphate provides phosphorus, muriate of potash (KCl) provides potassium, and gypsum (CaSO₄·2H₂O) is a soil conditioner providing calcium and sulfur, not primary NPK nutrients.