Which one of the following is used to induce artificial rain?

🔑Key Points:
The technique used in the formation of artificial rain is known as Cloud Seeding.
The chemist named Vincent J. Schaefer first invented artificial rain and snow.
Artificial rain also has synonyms like silviculture, artificial precipitation, rainmaking, etc.
The first country which used the technology of cloud seeding is the United Arab Emirates.
It is done with the help of the nucleation process. 
Nucleation is an initial process to form big crystals or molecules from small liquid solutions and vapors.
Silver iodide is generally used as a seeding agent in the formation of artificial rains.
These seeding agents are sprinkled or sprayed to introduce into the atmospheric clouds by airplanes or drones.
Silver iodide is a popularly used seeding agent because its molecular structure is the same as the structure of ice crystals.
On adding silver iodide into clouds it can work as small nuclei. 
Small nuclei of silver iodide attract small water droplets to form big water molecules which fall as rain on the earth.

🔴 Additional Information: Ammonium Chloride:
Ammonium chloride (NH4Cl) is a colorless white crystalline salt formed due to an acid-base reaction.
It is formed due to a reaction between sodium hydroxide (NH4OH) and hydrochloric acid (HCl).
It is used in various fields like as fertilizer in agriculture as a nitrogen source.
It is also used in the pharmaceutical industry, dry cells as electrolyte, oxide coating remover on metals, etc.

• Calcium carbonate:
 Calcium carbonate has the chemical formula CaCO3.
It is also known as calcite, limestone, or calcium salt.
It is a crystalline powder with having white color or colorless with no odor.
It is basically used in the construction field. 
Also used as a dietary supplement, as fertilizers, pharmaceutical industry, etc. 

• Potassium nitrate:
Potassium nitrate is an inorganic grey or white crystalline salt.
It has the formula KNO3.
It occurs naturally as a source of mineral nitrogen.
It is generally used in the preparation of explosives like fireworks, match sticks, etc.
It is also used in rocket fuels, fertilizers, dental use, etc.