Quote

Which pair of reagents will take part in a redox reaction (select one)?

1. CH3CHCH2 + Br2 (propene + bromine) 
2. CH3CH2CH2OH + conc. H3PO4 (propan-1-ol + conc. phosphoric acid)
3. CH3COCH3 + HCN (propanone + hydrogen cyanide) 
4. HCO2C2H5 + dil. H2SO4 (ethyl methanoate + dil. sulfuric acid)

At first, I (hastily) thought (4) was the redox reaction since H2SO4 is an oxidizing agent, however it turned out, according to the answer key, that (1) is the answer.

I don't understand how and why only (1) is an oxidizing agent.

For example, in (2) the oxidation number of the 2nd carbon increases and the 3rd carbon decreases.

And also in (3) 

Should I ignore the carbon when considering redox reactions on organic compounds? Or is my method wrong in any way?

 

I would assign oxidation numbers to carbon on the basis of ON(C) = (# of bonds to O, N, or X) -(# of bonds to H).  In some reactions, one carbon is oxidized while another is reduced, leading to no net oxidation or reduction.