Which of the following is the strongest reducing agent?

$H_2S$ is more acidic than $H_2O$,due to

Given below are two statements:
Statement $I$: Oxygen being the first member of group $16$ exhibits only $-2$ oxidation state.
Statement $II$: Down the group $16$ stability of $+4$ oxidation state decreases and $+6$ oxidation state increases.
In the light of the above statements,choose the most appropriate answer from the options given below:

Identify the correct statements from the following:
$i$. Sulphuric acid is manufactured by contact process.
$ii$. $SO_3$ dissolves in $H_2SO_4$ to form pyrosulphuric acid $(H_2S_2O_7)$.
$iii$. $H_2SO_4$ is used in the manufacture of fertilisers such as ammonium sulphate and super phosphate.
$iv$. In the reaction,$S + 2H_2SO_4 (\text{conc.}) \longrightarrow 3SO_2 + 2H_2O$,$H_2SO_4$ is oxidised to $SO_2$.

Caro's acid is

Which of the following oxoacids of sulfur contains a sulfur-sulfur $(S-S)$ double bond?