Question

Why is aldehyde a reducing agent?

Answer 1

Because it can be easily oxidized.

Explanation:

The formal oxidation state of the ipso carbon in an aldehyde, `R-C(=O)H` is `+I`; it can undergo oxidation to the carboxyl group, `RC(=O)OH`, where the ipso carbon has an oxidation number of `+III`. Of course, to fully oxidize the ipso carbon, to `+IV`, we have to break the carbon chain to give `CO_2`.