Which characteristic is commonly associated with nucleophiles?

Nucleophiles are species that have a tendency to donate electrons to form chemical bonds. A key characteristic of nucleophiles is the presence of lone pairs of electrons, which they can use to attack electrophiles (electron-deficient species). The lone pairs make nucleophiles reactive, as they can be involved in chemical reactions by facilitating the formation of new bonds. For instance, in nucleophilic substitution reactions, the nucleophile will use its lone pair to replace a leaving group on a substrate.

While some nucleophiles can be negatively charged, many are neutral molecules that possess lone pairs, such as water or ammonia. Therefore, the presence of lone pairs, regardless of charge, is a defining feature of nucleophiles, making this characteristic particularly relevant in organic chemistry and reaction mechanisms.

The other characteristics mentioned do not accurately describe nucleophiles. Having a positive charge suggests an electron-deficient species, which generally acts as an electrophile rather than a nucleophile. Being a good acid relates to the ability to donate protons (H+), not electrons. Likewise, saying nucleophiles are always neutral does not capture the full range of possible nucleophiles, which can include negatively charged ions as well.