Which of the following compounds undergoes aldol condensation?

How many aldol products (excluding stereoisomers) are obtained in the given reaction?
$CH_3-CH_2-CHO + C_6H_5CHO \xrightarrow[0-5 \ ^{\circ}C]{OH^{\ominus}} ?$

Which of the following reactions uses sodium cyanide $(NaCN)$ as a catalyst?

What is the percentage of formaldehyde in formalin (in $\%$)?

Consider the following sequence of reactions. The incorrect statement about $R$ is:

Compounds $P$ and $R$ upon ozonolysis produce $Q$ and $S$,respectively. The molecular formula of $Q$ and $S$ is $C_8H_8O$. $Q$ undergoes Cannizzaro reaction but not haloform reaction,whereas $S$ undergoes haloform reaction but not Cannizzaro reaction.
$(i)$ $P \xrightarrow[\text{ii) } Zn / H_2O]{\text{i) } O_3 / CH_2Cl_2} \underset{(C_8H_8O)}{Q}$
$(ii)$ $R \xrightarrow[\text{ii) } Zn / H_2O]{\text{i) } O_3 / CH_2Cl_2} \underset{(C_8H_8O)}{S}$
The option$(s)$ with a suitable combination of $P$ and $R$,respectively,is(are):