Silver iodide is used for producing artificial rain because $AgI$ :
A. is easy to spray at high altitude
B. is insoluble in water
C. is easy to synthesize
D. has crystals similar to ice

Hint: In artificial rain we add some chemicals or external agents that increase precipitation through clouds. The chemical particles which are drenched over clouds are dry Ice(solid carbon dioxide), Silver Iodide ( $AgI$ ), Salt powder etc. This process is known as Cloud Seeding.Cloud seeding is very popular nowadays because of the dryness of areas. Government is also taking steps to improve this process as it is helpful in farming. It is done by planes or rockets. These agents act as an ice nucleus and cause ice crystals to form and grow on their surface.

Complete step by step solution:

Silver iodide is used for producing artificial rains because when $AgI$ is sprayed over clouds it causes water droplets of clouds to coalesce to form bigger water drops and induce rains. The crystals grow rapidly by taking moisture from the surrounding water droplets, when they become heavy their weight causes them to fall. While falling, the crystals drops may melt and join with small liquid water droplets; they then form into raindrops in a manner similar to the artificial rain process.

So option D (has crystals similar to ice) is correct.

Note: We have approached this problem by giving this logic that $AgI$ has a crystal structure similar to ice. Hence, $AgI$ acts as an ice nucleus and causes ice crystals to form and grow. Silver iodide increases the number of cloud condensation nuclei around (CCN) which water vapor may form microscopic water droplets. This is why silver iodide is used in artificial rains.