Which of the following oxyacids of sulphur contains an $S-S$ linkage?

Observe the following statements :
$a$. The thermal stability of hydrides of group $16$ elements follows the order :
$H_2O > H_2S > H_2Se > H_2Te$
$b$. Acidic nature of hydrides of group $16$ elements follows the order :
$H_2O < H_2S < H_2Se < H_2Te$
$c$. The reducing nature of $H_2S$,$H_2Se$ and $H_2Te$ follows the order :
$H_2S < H_2Se < H_2Te$
The correct statements are:

When conc. $H_{2}SO_{4}$ is heated with $P_{2}O_{5}$,the acid is converted into

Which of the following compounds is most acidic in nature?

Which of the following statements regarding ozone $(O_3)$ is not correct?

Which of the following has the highest number of oxo groups?