Which one of the following is most acidic?

How many total statements are correct in the following?
$(i)$ $SO_2$ - antichlor,preservative
$(ii)$ $O_3$ - Disinfectant
$(iii)$ $Cl_2$ - Antiseptic
$(iv)$ $O_2$ - used in oxy-acetylene welding
$(v)$ $PH_3$ - used in smoke screens
$(vi)$ $HNO_3$ - Pickling of stainless steel

$H_2S$ is more acidic than $H_2O$,due to

Explain why ozone $(O_3)$ is thermodynamically less stable than oxygen $(O_2)$?

Which of the following hydrides is the most acidic?

Provide information about the allotropes of sulfur.