Which definition fits a Lewis base?

A Lewis base is defined as a substance that donates a pair of electrons to form a covalent bond. This definition is part of the Lewis theory of acids and bases, which expands on the traditional definitions by focusing on electron pair transfer rather than proton transfer. When a Lewis base donates an electron pair, it interacts with an electron pair acceptor, which is classified as a Lewis acid. This interaction is fundamental to many chemical reactions, including coordination complexes and various organic reactions, where the sharing and transfer of electrons are crucial.

This definition distinguishes Lewis bases from other types of bases, such as Brønsted-Lowry bases, which are characterized by their ability to accept protons (hydrogen ions). The Brønsted-Lowry theory focuses specifically on proton transfer, whereas the Lewis concept embraces a broader range of reactions involving electron pairs. Therefore, in the context of the question, the most suitable and accurate definition aligning with the concept of a Lewis base is that it is a substance that donates a pair of electrons.