The volume of oxygen liberated from $0.68 \ g$ of $H_2O_2$ is ............. $mL$ at $STP$.

$H_2O_2$ can be used as:

Phosphoric acid is preferred over sulphuric acid in preparing hydrogen peroxide from peroxides. Why?

Complete the following reactions:
$(i) \ O_2^{2-} + H_2O \to $
$(ii) \ O_2^- + H_2O \to $

$O_2F_2$ is an unstable yellow-orange solid and $H_2O_2$ is a colourless liquid. Both have an $O-O$ bond. The $O-O$ bond length in $H_2O_2$ and $O_2F_2$ respectively is:

Fill in the blanks:
$(1)$ $H_2O_2$ acts as an antiseptic, then it is known as ......... in the market.
$(2)$ Cation exchange resin is a ......... group containing organic molecule.
$(3)$ The ionic radius of $H^+$ ions and that of other ions is ......... $pm$ and ......... $pm$ respectively.
$(4)$ ......... group elements give salt-like hydrides.