The reactivity of carbonyl compounds (aldehydes and ketones) towards nucleophilic addition depends on two main factors:

1. Steric Hindrance: Nucleophilic attack is hindered by bulky groups attached to the carbonyl carbon. Therefore, reactivity decreases as the size of alkyl/aryl groups increases. Generally, Aldehydes > Ketones.
2. Electronic Effects: The reaction involves the attack of a nucleophile on the electron-deficient carbonyl carbon. Electron-withdrawing groups (EWG) like $-NO_2$ or $-I$ groups increase the positive charge on the carbon, increasing reactivity. Electron-donating groups (EDG) like alkyl groups ($+I$ effect) decrease the positive charge, decreasing reactivity.

Aromatic aldehydes are generally less reactive than aliphatic aldehydes due to resonance resonance stabilization of the carbonyl group with the benzene ring. However, an aromatic aldehyde with a strong electron-withdrawing group (e.g., p-Nitrobenzaldehyde) would be highly reactive.