Number of hydroxyl groups present in pyrosulphuric acid is

Pyrosulfuric acid, also known as oleum, has the chemical formula H₂S₂O₇. It is a powerful acid used in many industrial applications, including the production of detergents and dyes.

The structure of pyrosulfuric acid contains two sulfur atoms, seven oxygen atoms, and two hydrogen atoms. Each sulfur atom is bonded to three oxygen atoms and one hydrogen atom.

In the molecule, there are two hydroxyl (-OH) groups present, one attached to each sulfur atom. Therefore, the number of hydroxyl groups present in pyrosulfuric acid is 2.