The sum of oxygen atoms in the formulae of peroxydisulphuric acid and pyrosulphuric acid is

The laboratory test 'tailing of mercury' is used to identify:

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

Permono sulphuric acid is known as

Indicate the products $(X)$ and $(Y)$ in the following reactions:
$Na_{2}S + nS (n=1-8) \rightarrow (X)$
$Na_{2}SO_{3} + S \rightarrow (Y)$

Describe the physical properties of the elements of Group $16$.