Reduction of $>C=O$ to $CH_2$ can be carried out with:

Which of the following compounds is a hemiacetal?

Arrange the following compounds in the decreasing order of their reactivity towards nucleophilic addition reactions:
$(I) \, HCHO \, (II) \, CH_3CHO \, (III) \, CH_3COCH_3$

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):

$A$ strong base can abstract an $\alpha$-hydrogen from

In a set of the given reactions,acetic acid yielded a product $C$. Product $C$ would be:
$CH_3COOH + PCl_5 \to A$ $\xrightarrow{C_6H_6, \text{anh. } AlCl_3} B$ $\xrightarrow{C_2H_5MgBr, \text{ether}} C$