2.Which of the following compounds when dissolved in water will turn blue litmus paper red? copper oxide, calcium oxide, sulphur oxide, sodium oxide, iron oxide
All of the above oxides with the exception of sulphur oxide are basic oxides and so will not turn blue litmus paper red when dissolved in water. Sulphur oxide, SO2 on the other hand, is an acid anhydride (a non-metallic oxide which dissolves in water to produce acid) rendering it the ability of turning blue litmus paper red when dissolved in water.
All of the compounds except sulpher dioxide are metallic oxide which means basic oxide and base change red litmus paper to blue while acid change blue to red so the answer is the acidic oxide or sulpher dioxide
