Firstly H2SO4 is not a covalent compound its a ionic compound if we talk about SO4-2 ion that we come to valance bond theory and MOT as well . sulpher has 6 electrons in its outer most shell that gives 2p and 2s electrons so we can use maximum 6 electron an expand its valency to 2 to 6 during hybrydization as well.so it is your illusion that sulpher gives only valancy of two.

Introduction:
Sulfuric acid (H2SO4) is a covalent compound that consists of two hydrogen atoms, one sulfur atom, and four oxygen atoms. Although sulfur typically has a valency of 2, it can expand its valence shell and form more than two bonds by utilizing its empty d-orbitals. This ability to form multiple bonds allows sulfur to exhibit a valency greater than 2 in certain compounds, including H2SO4.

Sulfur's Expanded Octet:
Sulfur belongs to Group 16 of the periodic table, which means it has six valence electrons. To achieve a stable electron configuration, sulfur can share electrons and form covalent bonds. In the case of sulfuric acid, sulfur forms double bonds with two oxygen atoms, resulting in a total of four shared electrons. This leaves sulfur with two lone pairs of electrons and an expanded octet, allowing it to accommodate more than two bonds. The Lewis structure of H2SO4 clearly shows the double bonds between sulfur and oxygen.

Formation of Sulfuric Acid:
Sulfuric acid is commonly produced by the contact process, which involves several steps. Initially, sulfur dioxide (SO2) is oxidized to sulfur trioxide (SO3) using oxygen and a catalyst. This reaction occurs at high temperatures and is represented as follows:
2SO2 + O2 → 2SO3

The sulfur trioxide is then reacted with water to form sulfuric acid:
SO3 + H2O → H2SO4

Properties of Sulfuric Acid:
Sulfuric acid is a strong acid and is highly corrosive. It is colorless, oily, and dense, and has a molecular weight of 98.09 g/mol. It is soluble in water and dissociates into hydrogen ions (H+) and sulfate ions (SO4²-) when dissolved. The dissociation of sulfuric acid is as follows:
H2SO4 → 2H+ + SO4²-

Applications of Sulfuric Acid:
Sulfuric acid has numerous industrial applications. It is widely used in the production of fertilizers, detergents, and dyes. It is also utilized in the petroleum industry for refining and processing crude oil. Additionally, sulfuric acid is employed in the manufacturing of batteries, explosives, and pharmaceuticals. Due to its strong acidic nature, it is used for pH control in various chemical processes.

Conclusion:
Sulfuric acid (H2SO4) exists as a covalent compound despite sulfur's usual valency of 2. The ability of sulfur to expand its valence shell and form double bonds with oxygen allows it to exhibit a valency greater than 2 in H2SO4. This compound plays a crucial role in various industries and has significant applications in chemical processes.