What is the number of allotropes of selenium?

In the preparation of sulphuric acid,$V_2O_5$ is used in the reaction,which is:

What is produced by the dehydration of concentrated $H_2SO_4$ in the presence of $P_4O_{10}$?

Given below are two statements:
Statement $I$: The boiling points of the following hydrides of group $16$ elements increase in the order: $H_2O < H_2S < H_2Se < H_2Te$.
Statement $II$: The boiling points of these hydrides increase with an increase in molar mass.
In the light of the above statements,choose the most appropriate answer from the options given below:

What is produced by the hydrolysis of one mole of peroxodisulfuric acid $(H_2S_2O_8)$?

Oxygen is not evolved on reaction of ozone with