In the study of chemical reactivity, understanding the roles of nucleophiles and electrophiles is crucial. A nucleophile is a species that donates an electron pair to form a chemical bond, while an electrophile is an electron-deficient species that accepts an electron pair. To determine whether a molecule acts as a nucleophile or an electrophile, one can apply a specific rule based on the concept of dipoles and bonding preferences.

The key to this rule lies in identifying the side of the dipole with the highest bonding preference. This is determined by the number of bonds that the atoms can form. For instance, carbon, which can form four bonds, is more likely to act as an electrophile when it carries a positive charge, as it has a higher bonding preference compared to chlorine, which can only form one bond and carries a negative charge. Therefore, in a molecule where carbon is positively charged, it is classified as a good electrophile due to its ability to form multiple bonds.

Conversely, if a molecule is inert and does not react with other species, it cannot be classified as either a nucleophile or an electrophile. Such a molecule is described as non-reactive, indicating that it does not have a tendency to either donate or accept electrons.

To apply this understanding, one can analyze the remaining molecules in a given set by assessing their charges and bonding preferences. By identifying the atom with the highest bonding capability and its corresponding charge, students can effectively categorize the molecules as nucleophiles or electrophiles. This systematic approach simplifies the process of predicting chemical behavior in reactions.