Final answer:
Option a, 4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 5 H₂O(g), represents a balanced reaction.
Step-by-step explanation:
The chemical equation that represents a balanced reaction is option a.
4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 5 H₂O(g)
To determine if a chemical equation is balanced, you need to ensure that the number of atoms of each element is the same on both sides of the equation. In this case, there are 4 nitrogen (N) atoms, 10 hydrogen (H) atoms, and 10 oxygen (O) atoms on both sides, indicating a balanced reaction.