Which one of the following reactions will not result in the formation of a carbon-carbon bond?

The product $(A)$ of the following reaction is:

In the following reaction,
$CH_3-C \equiv CH$ $\xrightarrow[H_3O^+]{Hg^{2+}} X$ $\xrightarrow[PhCHO]{dil. NaOH} Y$
$X$ and $Y$,respectively,are

Identify the main product of the following reaction: $R - CO - O - R' \xrightarrow[H_3O^+]{DIBAL-H} \text{Product}$

Predict the products in the given reaction.

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....