Match the reactants in Column-$I$ with their corresponding products in Column-$II$.

The reaction sequence is as follows:
$HOOC-CH_2-CH_2-CH_2-CH_2-COOH$ $\xrightarrow[BaCO_3]{\Delta} A$ $\xrightarrow{NH_2-NH_2} B$ $\xrightarrow[KOH]{\text{heat}} C$
The final product $(C)$ obtained is:

Which of the following carbonyl compounds does $NOT$ undergo aldol condensation?

The reagent$(s)$ which can be used to bring about the following transformation is(are):
$(A)$ $LiAlH_4$ in $(C_2H_5)_2O$
$(B)$ $BH_3$ in $THF$
$(C)$ $NaBH_4$ in $C_2H_5OH$
$(D)$ Raney $Ni / H_2$ in $THF$

Complete reaction of acetaldehyde with excess formaldehyde,upon heating with conc. $NaOH$ solution,gives $P$ and $Q$. Compound $P$ does not give Tollens' test,whereas $Q$ on acidification gives positive Tollens' test. Treatment of $P$ with excess cyclohexanone in the presence of catalytic amount of $p$-toluenesulfonic acid $(PTSA)$ gives product $R$. Sum of the number of methylene groups $(-CH_2-)$ and oxygen atoms in $R$ is....

The compound obtained by the reduction of propionaldehyde by amalgamated zinc and concentrated $HCl$ is