Answer:
Oxygen gas (O₂)
Explanation:
Oxidizing agent is one which its self gets reduced and oxidizes the other.
Oxidation is the process where the oxidation number of substance increases while in reduction the oxidation number decreases.
The oxidation number of hydrogen in both methane and water is "+1"
Oxidation number of carbon in methane is "-4"
While its oxidation number in carbondioxide is "+4"
Thus carbon is undergoing oxidation.
While the change in oxidation number of oxygen from O₂ to CO₂ is "0" to -2
Hence it is undergoing reduction and oxidizing carbon.
