Question

An aqueous solution of which of the following oxides turn blue litmus red?
MgO,SO2,CaO

Answer 1

We know that metallic oxides are basic in nature, while non metallic oxides are acidic in nature. Thus, from your question, it is evident that Mg and Ca are metals, thus their oxides will be basic, while the oxide of sulphur (which is a non metal) would be acidic in nature.

Now, from our previous knowledge, we know that acids in their aqueous form dissociate hydrogen ions due to which they turn blue litmus red.

Hence, your answer is SO2!

Hope it helped!