The balanced reaction that shows incomplete combustion is option B:
B. C₂H₂ + 8O₂ → 6CO₂ + 5H₂O
In incomplete combustion, the reactant does not completely react with oxygen, resulting in the formation of carbon monoxide (CO) instead of carbon dioxide (CO₂). Option B demonstrates this by showing the formation of CO (carbon monoxide) along with water (H₂O) as the products.