An acidic oxide is a type of oxide that reacts with water to form an acid. In other words, an acidic oxide has the ability to donate hydrogen ions (protons) to form an acid.
One example of an acidic oxide is sulfur dioxide (SO2). When sulfur dioxide reacts with water, it forms sulfuric acid (H2SO4), which is a strong and highly corrosive acid.
SO2 + H2O → H2SO4
So, the correct answer is SO2.