UPSC Prelims 2025Question 85Environment

Artificial way of causing rainfall to reduce air pollution makes use of

Options

Correct answer: a

Decision rule

Cloud-seeding agents work by mimicking ice crystal structure, so iodides qualify; nitrates and chlorides are fertiliser salts, never seeding agents.

(a) silver iodide and potassium iodide

Artificial rainfall, or cloud seeding, is a weather modification technique used to enhance precipitation. It is sometimes used to reduce air pollution by washing away particulate matter from the atmosphere.
Silver iodide (AgI) is the most commonly used agent in cloud seeding because its crystalline structure is similar to ice, which promotes ice nucleation in clouds, encouraging raindrop formation.
Potassium iodide (KI) is often used along with silver iodide to enhance the efficiency of the seeding process.
These substances help induce rainfall artificially, thus reducing air pollution by clearing the air.

(b) silver nitrate and potassium iodide – Incorrect: Silver nitrate is not typically used for cloud seeding.
(c) silver iodide and potassium nitrate – Incorrect: Potassium nitrate is not used in cloud seeding.
(d) silver nitrate and potassium chloride – Incorrect: Neither silver nitrate nor potassium chloride is standard in artificial rainfall techniques.

Substance	Role in Cloud Seeding
Silver iodide (AgI)	Ice nucleating agent to promote raindrop formation.
Potassium iodide (KI)	Enhances cloud seeding efficiency; aids dispersion.

Concept	Explanation
Cloud Seeding	Process of introducing substances into clouds to induce rainfall.
Ice Nucleation	Formation of ice crystals that promote precipitation in supercooled clouds.
Air Pollution Control	Artificial rainfall helps wash pollutants like dust, smoke, and particulate matter from the atmosphere.

Concept / Term	Explanation / Relevance
Cloud Seeding	A weather modification technique aimed at enhancing precipitation by introducing substances into clouds.
Silver Iodide (AgI)	Primary chemical used in cloud seeding due to its ice nucleation properties, mimicking natural ice crystals.
Potassium Iodide (KI)	Used alongside silver iodide to improve cloud seeding efficiency and dispersion.
Ice Nucleation	Process where particles act as nuclei for ice crystal formation, essential for rain formation in cold clouds.
Artificial Rainfall	Induced precipitation via cloud seeding, which can help reduce air pollution by washing out particulates.
Air Pollution Control	Artificial rainfall helps clear particulate matter, dust, and pollutants from the atmosphere.
Silver Nitrate	Chemical not commonly used in cloud seeding; mainly used in other industrial and medical applications.
Potassium Nitrate / Chloride	Not used in cloud seeding; commonly used as fertilizers or in other chemical processes.

Chemical Compound	Common Uses	Relevance to Artificial Rainfall (Cloud Seeding)	Remarks
Silver Iodide (AgI)	Cloud seeding, photographic film, antiseptics	Primary agent used for ice nucleation in cloud seeding	Key chemical in artificial rainfall
Potassium Iodide (KI)	Medical use (thyroid protection), chemical reagent, cloud seeding enhancer	Used alongside AgI to improve dispersion and efficiency	Supports cloud seeding process
Silver Nitrate (AgNO3)	Medical antiseptic, photography, analytical chemistry	Not used for cloud seeding	Different chemical behavior
Potassium Nitrate (KNO3)	Fertilizer, food preservation (curing agent), gunpowder	Not used in cloud seeding	Mainly agricultural/industrial use
Potassium Chloride (KCl)	Fertilizer, food additive, medical treatment for potassium deficiency	Not used in cloud seeding	Primarily agricultural/medical use