Explain the structure of the carboxylic group.

The carbon atom in the carboxyl group is $sp^{2}$ hybridized.
This results in a planar structure where the three bonds around the carbonyl carbon are at an angle of approximately $120^{\circ}$ to each other.
The carboxylic carbon is less electrophilic than the carbonyl carbon in aldehydes and ketones because of the resonance effect,where the lone pair of electrons on the hydroxyl oxygen atom is delocalized over the carbonyl group,reducing the partial positive charge on the carbon atom.