Which of the following reactions reduces oxygen to form water?

• A. N_2 + 3 H_2 ightarrow 2 NH_3
• B. C + O_2 ightarrow CO_2
• C. 2 Na + Cl_2 ightarrow 2 NaCl
• D. 2 H_2 + O_2 ightarrow 2 H_2O

Answer: (D)

Verified step by step guidance

1. Identify the species being reduced in each reaction by looking for oxygen gaining electrons or forming water.
2. Recall that reduction involves the gain of electrons, and oxygen is reduced when it forms water (H_2O).
3. Examine each reaction: in the first, nitrogen is reduced to ammonia; in the second, carbon is oxidized to carbon dioxide; in the third, sodium is oxidized to sodium chloride.
4. Focus on the reaction where oxygen is directly converted to water, which involves hydrogen gas reacting with oxygen gas.
5. Conclude that the reaction \$2\ H_2 + O_2 \rightarrow 2\ H_2O$ shows oxygen being reduced to water.