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

Which of the following statements is not correct?

Upon heating $KClO_3$ in the presence of a catalytic amount of $MnO_2$,a gas $W$ is formed. Excess amount of $W$ reacts with white phosphorus to give $X$. The reaction of $X$ with $HNO_3$ gives $Y$ and $Z$.
$(1)$ $W$ and $X$ are,respectively:
$[A]$ $O_3$ and $P_4O_6$
$[B]$ $O_2$ and $P_4O_6$
$[C]$ $O_2$ and $P_4O_{10}$
$[D]$ $O_3$ and $P_4O_{10}$
$(2)$ $Y$ and $Z$ are,respectively:
$[A]$ $N_2O_3$ and $H_3PO_4$
$[B]$ $N_2O_5$ and $HPO_3$
$[C]$ $N_2O_4$ and $HPO_3$
$[D]$ $N_2O_4$ and $H_3PO_3$
Give the answer of question $(1)$ and $(2)$.

The number of $S=O$ and $S-OH$ bonds present in peroxodisulphuric acid $(H_2S_2O_8)$ and pyrosulphuric acid $(H_2S_2O_7)$ respectively are:

Red hot iron absorbs $SO_2$ giving the product

Which of the following is the structure of the tetrathionate ion?