Previous Year Question
Artificial way of causing rainfall to reduce air pollution makes use of
silver iodide and potassium iodide
silver nitrate and potassium iodide
silver iodide and potassium nitrate
silver nitrate and potassium chloride
Correct Answer: A
Detailed Solution
This process of causing artificial rainfall is called cloud seeding.
In cloud seeding, minute particles are released into suitable clouds around which water vapour can condense or freeze.
The crystalline structure of silver iodide resembles that of ice crystals.
In supercooled clouds, silver iodide acts as an ice nucleus and promotes the formation of ice crystals.
Potassium iodide may also be used with silver iodide in cloud-seeding mixtures.
Therefore, among the given options, silver iodide and potassium iodide form the correct combination.
Dry ice, or solid carbon dioxide, is also used in certain types of cloud seeding.
Particles of salts such as sodium chloride may be used in the hygroscopic seeding of warm clouds.
Cloud seeding does not create clouds in a completely clear sky; suitable clouds containing sufficient moisture must already be present.
The resulting raindrops can carry particulate pollutants present in the atmosphere towards the ground as they fall.
This process is called wet deposition or the washout of pollutants by rainfall.
It may temporarily reduce the concentration of dust and fine particles in the air.
The success of cloud seeding depends on cloud type, temperature, humidity, wind and atmospheric conditions.
It is not a permanent substitute for emission control; long-term reduction of air pollution requires control at pollution sources.