In considering the reactivity of compounds towards nucleophilic addition reactions, two primary factors need to be evaluated: the positive character of the electrophilic center and the degree of steric hindrance. Electrophilic Character: The more positive the electrophilic center, the more reactive it is towards a nucleophile. This is typically observed in aldehydes, where the electron-withdrawing effect of the carbonyl group is not counterbalanced by additional alkyl groups. Steric Hindrance: As steric hindrance increases, reactivity decreases. Larger substituents around the electrophilic center can block the approach of the nucleophile, thus lowering the reaction rate. Given these considerations, aldehydes are generally more reactive than ketones due to less steric hindrance and a higher degree of positive charge on the carbonyl carbon. Between ketones, those with smaller alkyl groups are usually more reactive. Evaluate each compound based on these criteria to determine their relative reactivity in nucleophilic addition reactions.