In the following reaction:
$C_2H_2$ $\xrightarrow[HgSO_4 / H_2SO_4]{H_2O} (x)$ $\xrightarrow{\text{Tautomerisation}} CH_3-CHO$
$(x)$ is $:-$

$CaC_2 + 2D_2O \longrightarrow$ "$P$" $+ Ca(OD)_2$
In the above reaction,the product "$P$" is:

$2-$Hexyne gives $trans-2-$hexene on treatment with:

Acetylene reacts with $HCN$ in the presence of $Ba(CN)_2$ to yield

Give the reaction for the cyclization of ethyne,or the reaction for passing ethyne through a red-hot iron tube.

Identify the alkyne in the following sequence of reactions:
Alkyne $\xrightarrow{\text{H}_2, \text{Lindlar's catalyst}} A$ $\xrightarrow{\text{Ozonolysis}} B \text{ (only)}$
Given that $B$ is obtained from $\text{CH}_2=\text{CH}_2$ via the Wacker process.