Of the choices listed the 2 is the best option, however, I usually refer to the valence of oxygen as 2-.
You are correct. In chemical reactions, the valency of oxygen is most commonly observed as 2-. This means that oxygen tends to gain two electrons to achieve a stable electron configuration. Thank you for pointing that out.
The valency of oxygen is determined by the number of electrons it can gain, lose, or share in a chemical reaction. In this case, the correct answer is d.4. Oxygen is in Group 6A of the periodic table, which means it has 6 valence electrons. To achieve a stable electron configuration, oxygen tends to gain 2 electrons to complete its valence shell, resulting in an oxidation state of -2.
