During which of the following reactions will a gaseous product $NOT$ be produced?

What is the order of the $K_a$ value for $H_2O_2$?

$H_2O_2$ can be used as:

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.

Which statement is false about $H_2O_2$?

$25$ volume hydrogen peroxide means