$4 \ mL$ of '$X$ volume' $H_2O_2$ on heating gives $80 \ mL$ of oxygen at $STP$. The value of $X$ is:

$H_2O_2$ is

In which of the following reactions does $H_2O_2$ act as an oxidising agent (either in acidic,alkaline,or neutral medium)?
$(i)$ $2Fe^{2+} + H_2O_2 \rightarrow$
$(ii)$ $2MnO_4^{-} + 6H^{+} + 5H_2O_2 \rightarrow$
$(iii)$ $I_2 + H_2O_2 + 2OH^{-} \rightarrow$
$(iv)$ $Mn^{2+} + H_2O_2 \rightarrow$

Hydrogen peroxide acts both as an oxidising and as a reducing agent depending upon the nature of the reacting species. In which of the following cases $H_2O_2$ acts as a reducing agent in acidic medium?

Which substance does not speed up the decomposition of $H_2O_2$?

Blackened oil painting can be restored into original form by the action of :