Consider these intermediate chemical equations. cap c times s plus 1 half cap o sub 2 g rightarrow CO times g CO times g plus 1 half cap o sub 2 g rightarrow CO sub 2 times g How will oxygen appear in the final chemical equation?

Add the two equations: C(s) + ½ O₂(g) → CO(g) and CO(g) + ½ O₂(g) → CO₂(g). The CO appears on both sides, so it cancels; the two ½ O₂ portions combine to 1 O₂ on the reactant side. Therefore, oxygen appears as O₂(g) as a reactant, choice D.

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