Which of the following molecules exhibits the lowest thermal stability?

Which of the following statements is $NOT$ correct about ozone?

The oxoacid of sulphur that does not contain a bond between sulphur atoms is

Rhombic sulphur has the following structure:

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

The catalyst used in the manufacture of $H_2SO_4$ by the contact process is