Well the aldehyde is oxidized to a carboxylic acid......
Now I used standard assignments for oxidation numbers here. As always the sum of the formal oxidation numbers equals the charge on, the molecule; and for a neutral organic molecule this charge is ZERO. Again, as always, the oxidation reaction balances mass and charge.
And we can represent the reduction reaction as:
We add the two redox reactions together to eliminate the electrons. And thus we add
Which (I think!) is balanced with respect to mass and charge, as is required for any chemical reaction. What do we see in this reaction? The deep blue colour of
Sometimes, Benedict's reagent can oxidize primary alcohols (and sugars) all the way up to the acids. With all these discriminating reactions, these qualitative tests, it is a good idea to perform the test on a reagent whose identity you know, so that you can appreciate the results of a positive test.