Answer:
2 atoms of H in the products side
Step-by-step explanation:
3NO₂ + H₂O → NO + 2HNO₃
In product side: 3 N (1 from NO and 6 from nitric acid), 7 O (6 from nitric acid + 1 from NO), 2 H
In reactant side: 3 N, 7 O (6 from the dioxide + 1 from water) and 2 H