Question

Generally, metallic oxides are basic and non-metallic oxides are acidic in nature. Solution of which of the following oxides in water will change the colour of blue litmus to red?
A) Sulphur dioxide
B) Magnesium oxide
C) Iron oxide
D) Copper oxide

Answer 1

Hint: A chemical compound which contains at least one oxygen atom and the one other element is known as oxide. Metallic oxides are basic in nature and they are made of oxygen and metal. Non- metallic oxides can be formed by oxygen and non-metal.

Complete step by step answer:
There are two types of metallic oxides: basic and amphoteric oxide. Examples of metallic oxides are: BaO, ZnO, CaO, etc. When oxide reacts with water and the base is called basic oxide. When an oxide behaves as acid as well as the basic oxide then, it is called as amphoteric oxide. When a metal reacts with oxygen it leads to the production of metallic oxides.
$2Mg + {O_2} \to 2MgO$
$MgO + {H_2}O \to Mg{\left( {OH} \right)_2}$
When a non-metal reacts with oxygen it leads to the production of non -metallic oxides. Examples of non-metallic oxides are: $C{O_2},S{O_2},CO,{P_2}{O_5},etc.$ Usually, non-metallic oxides are acidic in nature. It is because when they are reacted with water it leads to the formation of the acidic solution.
$S{O_2} + 2{H_2}O \to {H_2}S{O_4} + 2H$
This can also be proven by the litmus paper test where metal oxides when reacting with water will form strong bases and turn red litmus paper to blue. Whereas, non-metal oxides react with water and form strong acids that turn blue litmus paper to red. Non-metallic oxides are acidic in nature and sulphur dioxide is an acidic gas.

Thus, the correct answer is A. i.e., Sulphur dioxide.

Additional Information: Sulphur-dioxide dissolved in water can be tested with litmus.
$SO_2 + 2H_2O \to H_2SO_4 + 2H$
Sulphuric acid is acid that turns blue litmus to red.

Note: Only sulphur dioxide will change blue to red be because its solution will be acidic in nature. This can easily be shown by adding water and a few drops of universal indicator to a container of the gas. There are common indicators like phenolphthalein, methyl red and bromothymol blue are used to indicate the pH ranges 8 to 10, 4.5 to 6, 6 to 7.5.