Q.Explain why the carbonyl carbon of an aldehyde or ketone is electrophilic, using the polarity of the $\text{C=O}$ bond and the hybridisation of the carbon.

The carbonyl carbon is $sp^2$ hybridised, forming three coplanar $\sigma$ bonds at $\approx 120^\circ$ and one $\pi$ bond to oxygen from its remaining unhybridised $p$ orbital. Because oxygen is considerably more electronegative than carbon, it attracts the $\pi$ (and to a lesser extent $\sigma$) bonding electrons more strongly, leaving the oxygen with a partial negative charge ($\delta^-$) and the carbon with a matching partial positive charge ($\delta^+$). This can be represented by a minor charge-separated resonance form, $\text{C}^+\text{-O}^-$, alongside the major neutral $\text{C=O}$ form.

Identify the hybridisation and geometry of the carbonyl carbon, then apply the electronegativity difference between C and O to locate the resulting bond dipole and partial charges.

Describing the carbonyl carbon as simply 'neutral' because the overall molecule has no net charge -- the relevant polarity is the LOCAL charge separation across the $\text{C=O}$ bond, not the molecule's overall charge.