Final answer:
A hydroxyl anion (OH−) acts as a base, accepting hydrogen ions in solution to form water and thus fits the definition of a base as a compound that accepts protons.
Step-by-step explanation:
A hydroxyl anion acts as a base. An anion is an atom with a negative charge. In the context of bases, a base is a compound that accepts hydrogen ions (H+) in solution. This definition fits the hydroxyl anion (OH−), which can accept a proton (H+) to form water (H₂O). Hydroxide ions are examples of anions that function as bases, and when dissolved in water, they produce hydroxide ions, thus increasing the solution's pH.
Ionic compounds, like NaOH, contain the hydroxide ion, OH−, which is what makes them basic. They are able to accept a proton from acids during a reaction to form water:
H+ + OH− → H₂O
This confirms that the correct answer to the question is C) group, as a hydroxyl group consists of an oxygen atom covalently bonded to a hydrogen atom and carries a negative charge, thus making it a hydroxyl anion when it is separated from a compound.