Which of the following is an example of a redox reaction?
A. CaO + H₂O → Ca(OH)₂
B. NH₃ + HCl → NH₄Cl
C. NaCl + AgNO₃ → AgCl + NaNO₃
D. Zn + 2HCl → ZnCl₂ + H₂
Answer: Option D
Solution (By JKSSB Mock Tests)
In Zn + 2HCl, Zn is oxidized (0 to +2) and H⁺ is reduced (+1 to 0). So it is a redox reaction. The other reactions are double displacement (A), combination without oxidation state change (B, D). Redox requires change in oxidation states.
Explanation:
Incomplete combustion due to insufficient oxygen produces carbon monoxide (CO) and/or soot (C). Complete combustion gives CO₂ and H₂O. CO is poisonous, binds to hemoglobin.
Explanation:
Polyethylene (polythene) softens on heating and hardens on cooling, so it is thermoplastic. Bakelite is thermosetting; rubber is elastomer; silk is natural polymer.
Explanation:
Reverse osmosis (RO) uses pressure to force water through a membrane that blocks dissolved salts and impurities. Distillation uses boiling/condensation. Chlorination and ozonation are disinfection methods, not for desalination.
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