Which among the following is a group $16$ element?

Peroxodisulphuric acid $(H_2S_2O_8)$ contains which of the following bonds?

Which of the following acids contains an $O-O$ bond?

What is formed by the reaction of phosphorus pentachloride with concentrated sulfuric acid?

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

Write the molecular formula of Marshall's acid.