H = +1, O = -2 & S = +6
For this compound you must follow the oxidation number rules.
Oxygen and hydrogen both follow the rules associated with oxidation numbers as neither of them are an exception in this case.
The rules I am talking about are; Hydrogen is always +1, except when it is bonded to a group 1 metal (alkali metal) Oxygen is always -2, expect when it is a peroxide. Where it is -1.
Sulfur must therefore balance the remaining charge as the ##H_2SO_4## molecule is neutral.
So, starting with oxygen. 4 x -2 = -8 (as there are 4 oxygens) 2 x +1 = +2 (as there are 2 hydrogens) Giving a running total of -8 + 2 = -6. The sulfur must balance this remaining negative charge. S = +6



