Final answer:
The worst nucleophile due to bulkiness is a tertiary carbon, which has three other carbon atoms attached, leading to steric hindrance that impedes nucleophilic attack.
Step-by-step explanation:
The type of carbon that makes the worst nucleophile because it is bulky is typically a tertiary carbon. A tertiary carbon atom is one that is attached to three other carbon atoms, which makes it sterically hindered and less accessible for nucleophilic attack. In organic chemistry, nucleophilicity is influenced by several factors, including charge, solvent, and steric hindrance. In the case of a bulky tertiary carbon, this steric hinderance is due to the presence of additional alkyl groups surrounding the carbon atom, which creates spatial congestion, impeding the approach and binding of a nucleophile to that carbon's positively charged or partially positively charged areas. Therefore, nucleophiles that are large or bulky typically have reduced reactivity, especially in reactions where they must approach a sterically encumbered electrophile, such as an SN2 reaction where inversion of stereochemistry occurs in a single step.