The oxoacid of sulphur which has a lone pair of electron on sulphur atom is:

\(H_2SO_3\)

The correct answer is option 2. \(H_2SO_3\).

The name of the given acids are:

1. \(H_2SO_4\): Sulphuric Acid
2. \(H_2SO_3\): Sulphurous Acid
3. \(H_2S_2O_7\): Pyrosulphuric Acid
4. \(H_2SO_5\): Peroxymonosulphuric acid

Where lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond and is often referred to as a nonbonding pair or pair. Lone pairs are found in the atom shell of the outermost electron.

Oxoacids are oxygen containing acids. Sulphur is known to form many oxoacids, such as \(H_2SO_4\), \(H_2SO_3\) etc. Sulphur shows a tetrahedral structure when coordinated with oxygen in sulphur oxoacids. Sulphur oxoacids typically contain at least one \(S = O\) bond and one \(S−OH\) bond. Terminal peroxide clusters, terminal \(S = S\), terminal and bridging oxygen atoms and chains \((−S−)_n\) are also observed in addition to \(S = S\) and \(S−OH\).

Sulphur oxyacids, which contains a single pair of sulphide electrons, is sulphuric acid \(H_2SO_3\). In which only 4 valence electrons are involved in bonding the remaining 2 electrons remain as a single pair of sulphur (Sulphur has six valence electrons). The structure of \(H_2SO_3\) will be :