It depends, many metal oxides are basic while most nonmetal oxides are acidic. Some oxides are also amphoteric, possessing both acidic and basic properties.
Iron oxide is not a base.
Aluminum oxide is classified as a metal oxide. Specifically, it is known as an amphoteric oxide, meaning it can react both as an acid (when combined with a base) and as a base (when combined with an acid).
Barium oxide is a base. It is an ionic compound that reacts with water to form a strong base, barium hydroxide.
Copper oxide is a base because it can accept protons (H+ ions) from acids, forming water. An alkali, however, specifically refers to a base that is soluble in water, while copper oxide is insoluble in water.
Copper oxide is a base, since it neutralises dilute acid.
The oxide of fermium is not known.
Oxygen oxide is not a real substance.
Calcium oxide is a BASE. An Alkali is a soluble base. Calcium oxide per se, is not very soluble.
Silver oxide is a basic compound because it contains the oxide ion (O2-), which can accept protons and therefore acts as a base by reacting with acids to form water and a salt.
Sodium oxide is a basic oxide. It reacts with water to form sodium hydroxide, which is a strong base.
NaOH is formed then. NaOH is a strong base.
Sodium oxide is considered a base because it reacts with water to form a strong base, sodium hydroxide. When dissolved in water, sodium oxide produces hydroxide ions that can accept protons, making it a base according to the Brønsted-Lowry definition.