Which of the following yields $H_2O_2$ upon oxidation?

$10 \, mL$ of $H_2O_2$ solution $(d = 1 \, g/mL)$ when reacted with $KI$ solution produced $0.5 \, g$ of iodine. Calculate the percentage purity of $H_2O_2$ .............. $\%$

The correct statements about $H_2O_2$ are:
$A$. Used in the treatment of effluents.
$B$. Used as both oxidising and reducing agents.
$C$. The two hydroxyl groups lie in the same plane.
$D$. Miscible with water.
Choose the correct answer from the options given below:

$H_2O_2$ is a

The correct statements from the following are:
$i$. $Ca(OH)_2$ is used in Clark's method of removal of temporary hardness of water.
$ii$. $100 \ mL$ of $10$ vol $H_2O_2$ on complete decomposition liberates $1 \ L$ of oxygen at $STP$.
$iii$. Urea can be added to the solution of $H_2O_2$ as stabilizer.

Decomposition of $H_2O_2$ is prevented by