Nucleophilic addition reactions are the correct answer when discussing the reactions of aldehydes and ketones. Let's break down the options and explain why nucleophilic addition reactions are the most suitable choice.

a) Substitution reaction:
Substitution reactions involve replacing an atom or group of atoms with another atom or group of atoms. This type of reaction is not typically observed in aldehydes and ketones. Aldehydes and ketones do not undergo substitution reactions because the carbon-oxygen double bond is not easily broken.

b) Electrophilic addition reaction:
Electrophilic addition reactions involve the addition of an electrophile to a molecule. While it is true that aldehydes and ketones can undergo electrophilic addition reactions, this is not the most common reaction observed for these compounds. Electrophilic addition reactions usually occur with compounds that have a carbon-carbon double bond, such as alkenes.

c) Nucleophilic addition reaction:
Nucleophilic addition reactions involve the addition of a nucleophile to a molecule. This is the most common type of reaction observed for aldehydes and ketones. The carbonyl carbon in aldehydes and ketones is electrophilic, meaning it is attracted to nucleophiles. Nucleophiles can attack the carbonyl carbon, leading to the formation of a new bond and the addition of the nucleophile to the molecule.

Nucleophilic addition reactions are important in many chemical transformations involving aldehydes and ketones. For example, nucleophilic addition of a primary amine to an aldehyde or ketone forms an imine or Schiff base, respectively. Additionally, nucleophilic addition of a secondary amine to an aldehyde or ketone forms a hemiaminal, which can further react to form an imine or an aminal.

Overall, the correct answer is c) nucleophilic addition reactions because this is the most common type of reaction observed for aldehydes and ketones.