The number of $S=O$ bonds present in sulphurous acid,peroxodisulphuric acid and pyrosulphuric acid,respectively are :

White silver surface turns black when $O_3$ is passed over it. This is due to the formation of

Assertion : There is a large difference between the melting and boiling points of $O$ and $S$.
Reason : It can be explained on the basis of their atomicity in $O_2$ and $S_8$ molecules.

$V_2O_5$ is useful as a catalyst in:

The oxoacid of sulphur which contains two sulphur atoms in different oxidation states is

Explain the nature of oxides of group-$16$ elements.