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 (oxidation number decreases).

Step2: Calculate O oxidation number in A

In $\ce{O2}$, oxidation number = 0; in $\ce{CO}$, O = -2. Decrease → oxidizing agent.

Step3: Calculate O oxidation number in B

In $\ce{O2}$, oxidation number = 0; in $\ce{SO2}$, O = -2. Decrease → oxidizing agent.

Step4: Calculate O oxidation number in C

In $\ce{O2}$, oxidation number = 0; in $\ce{OF2}$, O = +2. Increase → not oxidizing agent.

Step5: Calculate O oxidation number in D

In $\ce{O2}$, oxidation number = 0; in $\ce{Na2O2}$, O = -1. Decrease → oxidizing agent.

Step6: Calculate O oxidation number in E

In $\ce{O2}$, oxidation number = 0; in $\ce{MgO}$, O = -2. Decrease → oxidizing agent.

Answer:

C. $\ce{2 F2(g) + O2(g) → 2 OF2(g)}$