Which of the following compounds is used to convert acetaldehyde into acetaldehyde cyanohydrin?

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):

Match the following reactions in List-$I$ with their products in List-$II$.

List-$I$ (Reaction)	List-$II$ (Product)
$A$. $\text{Ketone} + NaBH_4$	$I$. $1^\circ$-alcohol
$B$. $\text{Ester} + LiAlH_4$	$II$. $3^\circ$-alcohol
$C$. $RMgX + \text{Ketone}$	$III$. $2^\circ$-alcohol
	$IV$. $\text{Alkane}$

Which of the following on reaction with Grignard reagent followed by hydrolysis forms a secondary alcohol?

In the following reaction, the major product $(H)$ is

Would you expect $benzaldehyde$ to be more reactive or less reactive in nucleophilic addition reactions than $propanal$? Explain your answer.