Which of the following is an example of a biofertilizer?
A. Urea
B. Ammonium sulfate
C. NPK
D. Rhizobium
Answer: Option D
Solution (By JKExamLibrary)
Biofertilizers are living microorganisms that enrich the soil quality. Rhizobium is a symbiotic bacterium found in the root nodules of leguminous plants that fixes atmospheric nitrogen. Urea, NPK, and ammonium sulfate are chemical fertilizers synthesized through industrial processes.
Explanation:
On boiling, soluble calcium bicarbonate decomposes: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. The precipitate is calcium carbonate (limestone/chalk). Magnesium bicarbonate similarly forms MgCO₃ or Mg(OH)₂. This removes Ca²⁺ and Mg²⁺ ions, softening the water. Permanent hardness (CaSO₄, CaCl₂) doesn't precipitate on boiling and needs chemical treatment.
Explanation:
In reaction C, H₂O₂ oxidizes PbS (black) to PbSO₄ (white), where oxygen atoms from H₂O₂ are added. H₂O₂ itself is reduced to H₂O. In reaction D, H₂O₂ oxidizes I⁻ to I₂; that is also oxidation. But the most straightforward oxidizing reaction among these is the restoration of old paintings (PbS → PbSO₄). Reaction A: H₂O₂ reduces O₃ (acts as reducing agent). Reaction B: H₂O₂ reduces Ag₂O. H₂O₂ can act as both oxidizing and reducing agent.
Explanation:
Silver bromide decomposes into silver and bromine on exposure to light. This is a photochemical decomposition reaction, where a single compound breaks down into two or more simpler substances. It is also a redox reaction (Ag⁺ reduced, Br⁻ oxidized). Photographic films use this property. Combination would be A + B → AB. Displacement is A + BC → AC + B. Neutralization is acid + base → salt + water.
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