Question

Sulphurous anhydride is:
A.\[S{O_3}\]
B.\[SO_4^{2 - }\]
C.\[SO_3^{2 - }\]
D.\[S{O_2}\]

Answer 1

Hint: The anhydride of any acid is the compound that is obtained by the elimination of water from that acid. Anhydrides of inorganic acids are commonly the oxides of non-metallic elements. So in this question, we have to remove water from sulphurous acid molecules to obtain sulphurous anhydride.

Complete answer:
The anhydride of any compound is obtained by the elimination of water. The acid anhydrides are defined as the chemical compounds which are derived by the elimination of water molecules from an acid molecule. In inorganic chemistry, acid anhydrides are usually referred to as acidic oxide.
In this question, we have to first find out the formula of sulphurous acid. The formula for sulphuric acid is \[{H_2}S{O_3}\] . We have to remove water from this molecule. This process is known as dehydration and can be represented by the following equation:
\[ \Rightarrow {H_2}S{O_3}\xrightarrow{{ - {H_2}O}}S{O_2} + {H_2}O\]
Thus we can say that the anhydride of sulphuric acid is sulphur dioxide.
In other words, we can say that by adding water to sulphur dioxide we will get sulphurous acid.
Sulphur dioxide has a linear structure and is highly reactive. It usually exists in gaseous form.

Thus we can say that the correct answer for the question is option (D).

Note:
The simplest way to find the anhydride of any compound is by subtracting a water molecule from its molecule. Thus by removing 2 hydrogens and one oxygen we are left with the anhydride’s molecular formula. We can also see the anhydride for bases by removing water molecules from their molecular formula.