What is the gas liberated when alkaline formaldehyde solution is treated with $H_2 O_2$?

Give the reaction of $I_2$ with $H_2O_2$ in the presence of a basic medium.

In basic medium,$H_{2}O_{2}$ exhibits which of the following reactions?
$A$. $Mn^{2+} \rightarrow Mn^{4+}$
$B$. $I_{2} \rightarrow I^{-}$
$C$. $PbS \rightarrow PbSO_{4}$
Choose the most appropriate answer from the options given below:

$A$ colourless liquid $A$ contains $H$ and $O$ elements only. It decomposes slowly on exposure to light. It is stabilised by mixing urea to store in the presence of light.
$(i)$ Suggest the possible structure of $A$.
$(ii)$ Write the chemical equation for its decomposition reaction in light.

Write one chemical reaction for the preparation of $D_2O_2$.

How many millilitres of $3 \% \left( \frac{w}{v} \right) H_2O_2$ solution is required to get $150 \ mL$ of oxygen at $STP$?