Ammonium iodide is an inorganic compound with the chemical formula NH₄I. It usually exists in the form of colorless to white crystals, has a pungent odor, is easily soluble in water, and is also soluble in alcohol. Ammonium iodide is a commonly used chemical reagent with a wide range of applications in industry, agriculture and medicine.

1. Organic synthesis: Ammonium iodide is a commonly used iodizing agent for the introduction of iodine atoms in organic synthesis. It can be used in the preparation of a variety of organic compounds, including pharmaceuticals, dyes, and other fine chemicals.

2. Photosensitive materials: In the photographic and printing industries, ammonium iodide is used to prepare certain types of photosensitive materials, such as photographic paper and film.

3. Electrochemistry: Ammonium iodide is an electrolyte that is used in electrochemical experiments such as electroplating and battery manufacturing. It is also used in the process of electrolysis of water to produce hydrogen.

4. Fertilizer: Ammonium iodide can be used as a trace element fertilizer to provide the iodine needed for plant growth and help prevent plant diseases caused by iodine deficiency.

5. Medicine: Ammonium iodide has a small number of applications in the pharmaceutical field, such as as as a precursor to radiotracer, or in some diagnostic procedures.

6. Analytical chemistry: In analytical chemistry, ammonium iodide can be used as a precipitant for the separation and detection of certain metal ions.

7. Salt iodization: Although not commonly used, ammonium iodide can be used as a method of salt iodization to prevent iodine deficiency diseases.

8. Laboratory reagents: Ammonium iodide is a commonly used chemical reagent in laboratories for teaching and scientific research purposes.