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:
Temporary hardness is due to Ca(HCO₃)₂ and Mg(HCO₃)₂. Upon boiling, these decompose into insoluble CaCO₃ and Mg(OH)₂, which precipitate out and can be filtered. Thus, boiling effectively removes temporary hardness, and R correctly explains the chemical mechanism involved.
Explanation:
MnO₂ oxidizes HCl (Cl⁻ to Cl₂) while itself being reduced (Mn⁴⁺ to Mn²⁺). Oxidizing agent (oxidant) accepts electrons and gets reduced. Here, MnO₂ accepts electrons from Cl⁻. HCl is the reducing agent (reductant) as it loses electrons. This reaction was used by Scheele to discover chlorine. Exam tip: The substance reduced is the oxidizing agent; the substance oxidized is the reducing agent.
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