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🧪 Chemistry  ·  Environmental Chemistry  ·  NEET & JEE

Dissolved oxygen in a river or lake is essential mainly for:

Answer: aquatic life.

  • A ordinary combustion
  • B aquatic life
  • C ozone formation
  • D smog production

Correct answer: B. aquatic life

Explanation: Fish and other aquatic organisms depend on dissolved oxygen for respiration.

Classical (London) SmogSources: coal burningSO₂ + particulates + fogReducing typeConditions: cold, humid,early morning, winterVisibility: very low (fog)London, 1952 - ~4000 deathsHarms: eyes, lungs, bronchitisPhotochemical (LA) SmogSources: vehicles, industriesNOx + hydrocarbons + UVOxidising typeConditions: warm, sunny,afternoon, summerProducts: O₃, PAN, acroleinLos Angeles (common in cities)Harms: eyes, rubber cracking

Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.

Concept context

Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.

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