Answer: C. A new compound formed when nitrogen and hydrogen chemically reacted.
Step-by-step explanation:
Due to the temperature increase, the atoms of both Nitrogen and Hydrogen reacted chemically with one another and formed a new compound which was still colorless but now had a strong odor as well.
This new compound is known as Ammonia with the chemical composition NH₃. It is formed when Hydrogen and Nitrogen react chemically. Ammonia is a colorless gas with a sharp strong odor.