by Q. Artificial way of causing rainfall to reduce air pollution makes use of:
UPSC Civil Services Examination (Prelims) 2025 – General Studies Paper I
(a) Silver iodide and potassium iodide
(b) Silver nitrate and potassium iodide
(c) Silver iodide and potassium nitrate
(d) Silver nitrate and potassium chloride
Answer: (a) Silver iodide and potassium iodide
Explanation:
Artificial rainfall, commonly known as cloud seeding, is used to induce precipitation and can help in reducing air pollution by washing out particulate matter and pollutants from the atmosphere. This method involves introducing certain chemicals into clouds to act as condensation or ice nuclei, around which water droplets or ice crystals can form and grow heavy enough to fall as rain.
Silver iodide (AgI) is the most widely used chemical in cloud seeding. Its crystal structure closely resembles that of ice, making it an effective ice-nucleating agent, especially in cold clouds.
Potassium iodide (KI) is often used along with silver iodide as a carrier or supporting agent to enhance dispersion.
Why other options are incorrect:
Silver nitrate (AgNO₃) is highly soluble and does not effectively mimic the ice lattice structure needed for cloud nucleation.
Potassium nitrate (KNO₃) and potassium chloride (KCl) are not efficient ice nuclei for inducing rainfall.
Other chemicals used in artificial rainfall:
Sodium chloride (NaCl): Commonly used in warm cloud seeding, especially in tropical regions like India. NaCl particles act as hygroscopic nuclei, attracting moisture and helping small water droplets merge into larger ones that fall as rain.
Dry ice (solid CO₂): Sometimes used to rapidly cool cloud regions, encouraging ice crystal formation.
Answer: (a) Silver iodide and potassium iodide
