In which of the following reactions is $H_2O_2$ acting as a reducing agent?

Which of the following reagents is known as Fenton's reagent?

$A$ compound $(MO_2)$ of a group $1$ element $(M)$ is hydrolyzed to form $M^{+}$,$OH^{-}$,$X$,and $Y$. When $X$ reacts with $I_2$ in a basic medium,the products formed are $I^{-}$,water,and $Y$. Then $X$ and $Y$ are respectively:

Which of the following statements is incorrect?

How many millilitres of $20$ volume $H_2O_2$ solution is needed to react completely with $500 \ mL$ of acidified $1 \ N \ KMnO_4$ solution?

$1 \ mL$ of "$x$ volume" $H_2O_2$ solution on heating gives $20 \ mL$ of oxygen gas at $STP$. The $(w/v) \%$ corresponding to "$x$ volume" of $H_2O_2$ is