Final answer:
The Lewis definition of an acid is a species that accepts a pair of electrons, hence the correct answer is (C) accepting a pair of electrons.
Step-by-step explanation:
According to the Lewis definition, an acid is a species that accepts a pair of electrons. Therefore, the answer to the question is (C) accepting a pair of electrons.
In contrast to the Brønsted-Lowry theory, which defines acids as proton donors, the Lewis theory considers an acid to be any substance that can accept an electron pair to form a covalent bond. Examples of Lewis acids include the hydrogen ion (H+), metal cations like Mg²+ and Zn²+, and neutral species such as boron trifluoride (BF3) and carbon dioxide (CO₂).