Oxidation of ammonia with CuO produces nitrogen gas and water vapor. This reaction is represented as:

2NH3 + 3CuO → 3Cu + N2 + 3H2O

The gaseous chemical produced in this reaction is nitrogen gas (N2), which is also obtained by reacting excess ammonia with chlorine. This reaction is represented as:

2NH3 + Cl2 → N2 + 2HCl

Explanation:

- Ammonium nitrate: Heating ammonium nitrate results in the decomposition of ammonium nitrate into nitrogen gas, water vapor, and oxygen gas. The reaction is represented as:

NH4NO3 → N2 + 2H2O + O2

- Potassium dichromate: Heating potassium dichromate results in the production of oxygen gas and potassium chromate. The reaction is represented as:

4K2Cr2O7 → 4K2CrO4 + 3O2

- Catalytic oxidation of ammonia: Catalytic oxidation of ammonia involves the use of a catalyst (such as platinum or palladium) to oxidize ammonia to nitrogen gas and water vapor. The reaction is represented as:

4NH3 + 5O2 → 4NO + 6H2O
2NO + O2 → 2NO2
4NO2 + O2 → 2N2O5
N2O5 → N2 + 2.5O2

- Reacting excess ammonia with chlorine: This reaction involves the reaction of excess ammonia with chlorine gas to produce nitrogen gas and hydrochloric acid. The reaction is represented as:

2NH3 + Cl2 → N2 + 2HCl

Therefore, option B, reacting excess ammonia with chlorine, is the correct answer.