Introduction:
Sulphuric acid (H2SO4) is a highly corrosive and dense liquid. It is commonly known as oil of vitriol due to its oily and viscous nature. This property sets it apart from most other acids. The unique characteristics of sulphuric acid can be attributed to its chemical structure and intermolecular forces.

Chemical Structure:
Sulphuric acid is composed of two hydrogen atoms, one sulphur atom, and four oxygen atoms. It has a molecular formula of H2SO4. The acidic nature of sulphuric acid is due to the presence of hydrogen ions (H+) that can dissociate in water.

Intermolecular Forces:
The viscosity and oily nature of sulphuric acid can be explained by the intermolecular forces present in the liquid. Intermolecular forces are the attractive forces between molecules. In the case of sulphuric acid, the dominant intermolecular force is hydrogen bonding.

Hydrogen Bonding:
Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen). In sulphuric acid, the oxygen atoms form hydrogen bonds with hydrogen atoms from neighboring molecules. These hydrogen bonds create strong intermolecular attractions, resulting in a higher viscosity and a more cohesive liquid.

Viscosity:
Viscosity refers to a liquid's resistance to flow. In the case of sulphuric acid, the hydrogen bonding between molecules leads to a high degree of molecular cohesion. The hydrogen bonds restrict the movement of the molecules, making it difficult for them to flow freely. Consequently, sulphuric acid exhibits a higher viscosity compared to many other liquids.

Oily Nature:
The oily nature of sulphuric acid is a result of its high density and cohesive properties. The strong intermolecular forces, particularly hydrogen bonding, cause the molecules to stick together and form a cohesive liquid. This cohesive nature gives sulphuric acid a thick and oily consistency.

Conclusion:
Sulphuric acid's oily and viscous nature can be attributed to its chemical structure and the intermolecular forces, particularly hydrogen bonding, present in the liquid. These characteristics make sulphuric acid a unique and distinctive acid among others.