Which of the following gas mixtures is used by divers inside the sea?

Which of the following statements are correct?
$i$. The basic structural unit of silicates is $SiO_4^{4-}$
$ii$. Silicones are biocompatible
$iii$. Producer gas contains $CO$ and $N_2$
The correct option is

Observe the following reactions (unbalanced):
$P_2O_3 + H_2O \rightarrow X$
$P_4O_{10} + H_2O \rightarrow Y$
The number of $P=O$ bonds present in $X$ and $Y$ are respectively:

When lead nitrate is heated,it gives

Dry bleaching is done by

Which products are obtained when $AgNO_3$ is strongly heated?