2.)
a.) As we progress across the reaction scheme from methane to carbon dioxide, the carbon atom is being oxidized at every step of the way. In general terms, oxidation is the loss of electrons that leads to a higher oxidation state. In organic chemistry, the same principles apply, however, we typically mean forming more bonds to oxygen when referring to oxidation with these molecules. As we progress from methane to carbon dioxide, the central carbon atom is gaining a new bond to oxygen in each molecule. As carbon gains a bond to oxygen, its oxidation state increases by 2.
In CH₄, the oxidation state of carbon is -4. As we add a bond to oxygen to form CH₃OH, the oxidation state becomes -2. Adding another bond to oxygen to get formaldehyde, HCOH, gives carbon an oxidation state of 0. This trend continues as we form three bonds to carbon in formic acid, where the carbon has an oxidation state of +2, and finally the carbon has an oxidation state of +4 in carbon dioxide.
b.) Formaldehyde could be used as a molecule that can either be oxidized or reduced. We just demonstrated that the oxidation state of carbon can range from -4 to +4. The central carbon of formaldehyde has an oxidation state of 0, therefore, it could be readily oxidized or reduced as it falls in the middle of the possible oxidation states of carbon.
c.) Based purely on the oxidation states, and not on the real world reactivities of these molecules, the molecule that would be most likely to be reduced would be carbon dioxide. The carbon atom of CO₂ has an oxidation state of +4. Therefore, it cannot be oxidized any further and can only be reduced.
d.) Again, based purely on these oxidation states, methane is the most likely candidate to be oxidized. The carbon at of methane has an oxidation state of -4, making it the lowest oxidation state possible for carbon. This carbon atom can only be oxidized further.
