From the given list, the number of compounds with + 4 oxidation...

The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom is known as the Oxidation Number.

In ${H}_{2}{SO}_{3}$

 Let the oxidation number of S be x.

$2 ( + 1 ) + x + 3 ( - 2 ) = 0x = + 4$ 

Similarly the $+ 4$oxidation state of sulphur is shown by ${SOCl}_{2}and{SF}_{4}$.

$\begin{cases}\text{Compounds} & {SO}_{3} & {H}_{2}{SO}_{3} & {SOCl}_{2} & {SF}_{4} & {BaSO}_{4} & {H}_{2}{S}_{2}{O}_{7} \\ \text{O.S.of Sulphur:} & + 6 & + 4 & + 4 & + 4 & + 6 & + 6\end{cases}$