H2SO4 and CaCl2 are not suitable for drying ammonia gas because they react with the gas. Ammonia is a basic gas, and both H2SO4 and CaCl2 are acidic. When these two substances react, they form salts that contain ammonia. This can contaminate the ammonia gas and make it unusable. In addition, H2SO4 is a corrosive substance, and CaCl2 can be harmful to breathe in. Therefore, it is not safe to use these substances to dry ammonia gas.