Solution:
Sulphur dioxide is the oxide in which water will change the colour of blue litmus to red.Generally metallic oxides are basic and non-metallic oxides are acidic in nature. Metals generally react with oxygen to form basic oxides, while non-metals react with oxygen to form either acidic or neutral oxides. Out of all these, only sulphur is non-metal. Therefore it forms an acidic oxide which, when put on a blue litmus, changes its colour to red. In comparison, all the basic oxides change the colour of red litmus to blue.
Reaction:
