Which statement best describes a Lewis base?

Which statement best describes a Lewis base?

• A. Donates an electron pair.
• B. Accepts an electron pair.
• C. Donates a proton.
• D. Increases acidity.

Answer: (A)

In Lewis acid–base theory, a base is defined as an electron-pair donor. That means the key action of a Lewis base is to supply a lone pair to form a bond with an electron-poor partner, often a Lewis acid. So the statement that donates an electron pair captures the essence of being a Lewis base. For example, ammonia has a lone pair on nitrogen and can donate that pair to a proton or to boron in boron trifluoride, creating a coordinate covalent bond. The other ideas describe different concepts: accepting an electron pair would describe a Lewis acid, donating a proton is a Brønsted–Lowry concept focused on proton transfer, and increasing acidity relates to how substances influence pH rather than the electron-pair donation property that defines a Lewis base.

In Lewis acid–base theory, a base is defined as an electron-pair donor. That means the key action of a Lewis base is to supply a lone pair to form a bond with an electron-poor partner, often a Lewis acid. So the statement that donates an electron pair captures the essence of being a Lewis base. For example, ammonia has a lone pair on nitrogen and can donate that pair to a proton or to boron in boron trifluoride, creating a coordinate covalent bond. The other ideas describe different concepts: accepting an electron pair would describe a Lewis acid, donating a proton is a Brønsted–Lowry concept focused on proton transfer, and increasing acidity relates to how substances influence pH rather than the electron-pair donation property that defines a Lewis base.