Which of the following reactions is a combination redox reaction?

• A. Zn + CuSO_4 ightarrow ZnSO_4 + Cu
• B. 2H_2 + O_2 ightarrow 2H_2O
• C. 2KClO_3 ightarrow 2KCl + 3O_2
• D. AgNO_3 + NaCl ightarrow AgCl + NaNO_3

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what a combination redox reaction is. A combination reaction is one where two or more reactants combine to form a single product. A redox reaction involves the transfer of electrons, meaning one species is oxidized and another is reduced.
2. Step 2: Analyze each reaction to see if it fits the criteria of a combination reaction (multiple reactants forming one product) and if it involves electron transfer (redox).
3. Step 3: For the reaction \(\mathrm{Zn + CuSO_4 \rightarrow ZnSO_4 + Cu}\), note that zinc is oxidized and copper is reduced, but the products are two separate compounds, so it is not a combination reaction.
4. Step 4: For the reaction \(\mathrm{2H_2 + O_2 \rightarrow 2H_2O}\), two reactants combine to form a single product, and hydrogen is oxidized while oxygen is reduced, so this is a combination redox reaction.
5. Step 5: For the other reactions, \(\mathrm{2KClO_3 \rightarrow 2KCl + 3O_2}\) is a decomposition reaction, and \(\mathrm{AgNO_3 + NaCl \rightarrow AgCl + NaNO_3}\) is a double displacement reaction without redox changes. Therefore, only the hydrogen and oxygen reaction fits the combination redox criteria.