To dry ammonia gas, various drying agents can be used to remove moisture from the gas. Among the options provided, anhydrous CaCl2 is the most suitable drying agent for ammonia.

- Anhydrous CaCl2 is a common drying agent used to remove moisture from gases.
- When ammonia gas comes in contact with anhydrous CaCl2, the CaCl2 absorbs the moisture present in the gas.
- The moisture is converted into a hydrated form of CaCl2, leaving the ammonia gas dry.

- Anhydrous CaCl2 is preferred for drying ammonia because it has a high affinity for water and can effectively remove moisture from the gas.
- It is easily available and inexpensive, making it a cost-effective drying agent.
- Anhydrous CaCl2 can be regenerated by heating it to remove the absorbed moisture, allowing it to be reused multiple times.
In conclusion, drying ammonia gas using anhydrous CaCl2 is a simple and effective method to ensure the gas is free of moisture, making it suitable for various industrial applications.