Which item is not nucleophilic? a proton a carbanion an imidazole?

The term "nucleophilic" describes substances that have excess electron pairs that they want to donate or share.

A proton does not have any excess electron pairs, so it is not nucleophilic.

A carbanion has a pair of excess electrons on a carbon atom, so it is nucleophilic.

An imidazole has excess electrons on its nitrogen atom, so it is nucleophilic.

Therefore, only the proton is not nucleophilic.