Question

oxygen is acting as an oxidizing agent in all of the following reactions except
a. $ce{2 c(s) + o_{2}(g) -> 2 co(g)}$
b. $ce{s(s) + o_{2}(g) -> so_{2}(g)}$
c. $ce{2 f_{2}(g) + o_{2}(g) -> 2 of_{2}(g)}$
d. $ce{2 na(s) + o_{2}(g) -> na_{2}o_{2}(s)}$
e. $ce{2 mg(s) + o_{2}(g) -> 2 mgo(s)}$

Explanation:

Step1: Define oxidizing agent role

An oxidizing agent is reduced (gains electrons, oxidation number decreases).

Step2: Calculate O oxidation number in each reaction

• Reaction A: O in $\text{O}_2$ is 0; in $\text{CO}$ is -2. Oxidation number decreases.
• Reaction B: O in $\text{O}_2$ is 0; in $\text{SO}_2$ is -2. Oxidation number decreases.
• Reaction C: O in $\text{O}_2$ is 0; in $\text{OF}_2$ is +2. Oxidation number increases.
• Reaction D: O in $\text{O}_2$ is 0; in $\text{Na}_2\text{O}_2$ is -1. Oxidation number decreases.
• Reaction E: O in $\text{O}_2$ is 0; in $\text{MgO}$ is -2. Oxidation number decreases.

Step3: Identify non-oxidizing agent case

Only in reaction C, oxygen is oxidized (loses electrons), so it is not an oxidizing agent.

Answer:

C. $2\ \text{F}_2(\text{g}) + \text{O}_2(\text{g})
ightarrow 2\ \text{OF}_2(\text{g})$