The oxoacid of sulphur that does not contain bond between sulphur atoms is:

Concept:

Oxoacids are basically the acids that contain oxygen. Sulphur is known to form many oxoacids. In oxoacids of sulphur, Sulphur exhibits a tetrahedral structure when coordinated to oxygen. Generally, oxoacids of sulphur contain at least one S=O bond and one S-OH bond. Terminal peroxide groups, terminal S=S, terminal and bridging oxygen atoms and chains of (-S-)_n are also observed in addition to S=S and S-OH.

H₂S₂O₃ is called as Thiosulfuric acid. The oxidation number is −2 (for the terminal sulphur), +6 (for the central atom). Since sulphur contains bond between sulphur atoms.

H₂S₂O₄ is called as Dithionous acid. The oxidation number is +3 and the structure has two sulphur bonding between each other.

H₂S₄O₆ is called as polythionic acid. The oxidation number is 0 (for the bridging S atoms), +5 (for the terminal central S atoms). It also contains sulphur bond between them.

H₂S₂O₇ does not show bonding between sulphur atoms.

Pyrosulphuric acid (H₂S₂O₇) is also known as oleum. It is an anhydride of sulphuric acid, it is a colourless, crystalline solid and has a melting point of 36°C. It can be prepared by reacting excess sulphur trioxide with sulphuric acid. The reaction goes like this:

H₂SO₄ + SO₃ → H₂S₂O₇

It reacts with bases to form salts which are called pyrosulphates.

Pyro sulphuric acid (H₂S₂O₇) is a strong acid which is a main constituent of fuming sulfuric acid (oleum). It is also commonly known as disulphuric acid.