📘 IAS Prelims 2025 — GS-I | Q.85 | Classroom Explanation
(Environment & Ecology | Atmospheric Processes)

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📌 Question

Q.85)
Artificial way of causing rainfall to reduce air pollution makes use of:

(a) Silver iodide and potassium iodide
(b) Silver nitrate and potassium iodide
(c) Silver iodide and potassium nitrate
(d) Silver nitrate and potassium chloride

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✅ Correct Answer: (a) Silver iodide and potassium iodide

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🧑‍🏫 Classroom Explanation

Artificial rainfall is achieved through a scientific process known as cloud seeding 🌧️.
It is often discussed in the context of air pollution mitigation, drought management, and water security.

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🌫️ What is Cloud Seeding?

Cloud seeding involves introducing specific chemicals into clouds to stimulate precipitation.
The idea is simple:

➡️ Provide artificial nuclei around which water vapour can condense or freeze
➡️ This accelerates rainfall or snowfall

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🧪 Why Silver Iodide (AgI)?

• Silver iodide has a crystal structure similar to ice ❄️
• Acts as an ice nucleus
• Encourages supercooled water droplets to freeze and fall as precipitation

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🧂 Role of Potassium Iodide (KI)

• Works as a supplementary nucleating agent
• Enhances the efficiency of cloud seeding
• Sometimes used along with silver iodide in warm cloud conditions

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🌬️ How Does It Help Reduce Air Pollution?

• Artificial rain helps:
  • Wash out particulate matter (PM2.5, PM10) from the atmosphere
  • Reduce smog episodes, especially in urban and industrial regions
• Often attempted during severe pollution episodes (e.g., Delhi NCR experiments)

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❌ Why Other Options Are Incorrect?

• Silver nitrate ❌
  • Used in chemistry and medicine, not effective as ice nuclei
• Potassium nitrate / potassium chloride ❌
  • Fertilizer / salt compounds, not suitable for cloud microphysics

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🧠 One-Line Memory Hook (Prelims Gold)

“Cloud seeding rains fall on silver iodide crystals.”

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📍 GS Mapping

Atmospheric phenomena and human intervention

GS Paper I

Environment & Ecology

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