Which of the following reactions is NOT a redox reaction?
A. 2Na + Cl₂ → 2NaCl
B. CH₄ + 2O₂ → CO₂ + 2H₂O
C. Zn + CuSO₄ → ZnSO₄ + Cu
D. CaCO₃ → CaO + CO₂
Answer: Option D
Solution (By JKExamLibrary)
In CaCO₃ decomposition, the oxidation states are: Ca (+2), C (+4), O (-2) in both reactant and products, so no change—not a redox reaction. The others involve changes: Zn(0→+2), Cu(+2→0) in B; Na(0→+1), Cl(0→-1) in C; C(-4→+4), O(0→-2) in D. Redox requires change in oxidation numbers.
Explanation:
Joseph Proust proposed the law of definite proportions (constant composition) – a given compound always contains the same elements in the same proportion by mass. Dalton's theory explained it. Lavoisier gave law of conservation of mass. Rutherford discovered nucleus.
Explanation:
Excessive use of chemical fertilizers, especially those containing nitrogen and phosphorus, can lead to runoff into water bodies. This causes eutrophication (algal blooms), which depletes oxygen in the water and kills aquatic life. It also degrades soil health and kills beneficial microbes over time.
Explanation:
Hard water contains dissolved Ca²⁺ and Mg²⁺ ions which react with soap to form insoluble scum, preventing lather. Soft water lathers readily. Distilled water is pure (soft). Rainwater is naturally soft but may dissolve CO₂ and become slightly acidic.
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