Final answer:
The correct answer is option B. Reaction B "C + O2 → CO2" exemplifies a synthesis reaction where carbon and oxygen combine to create carbon dioxide.
Step-by-step explanation:
The question posed focuses on identifying which of the given reactions is a synthesis reaction. A synthesis reaction occurs when two or more reactants combine to form a single new product.
Among the options presented, reaction B "C + O2 → CO2" represents a synthesis reaction since carbon (C) and oxygen (O2) combine to form carbon dioxide (CO2), whereas other options illustrate different types of chemical reactions, like single replacement, decomposition, and double replacement reactions.