Explanation:

All codes are correct.

• The most common chemicals used for cloud seeding include silver iodide, potassium iodide, dry ice (solid carbon dioxide) and Liquid propane.

• Clouds are made up of tiny water droplets or ice crystals that form when water vapor in the atmosphere cools and condenses around a tiny particle of dust or salt floating in the atmosphere.

• Without these particles, known as condensation or ice nuclei, raindrops or snowflakes cannot form and precipitation will not occur.

• Cloud seeding is a weather modification technique that improves a cloud’s ability to produce rain or snow by introducing tiny ice nuclei into certain types of subfreezing clouds.

• These nuclei provide a base for snowflakes to form.

• After cloud seeding takes place, the newly formed snowflakes quickly grow and fall from the clouds back to the surface of the Earth, increasing snowpack and streamflow.

Hence option 4th is correct.