Identify $A$ in the following reaction.
$A$ $\xrightarrow{\text{Lithium amide}} \text{Ethynyl lithium}$ $\xrightarrow{\text{Bromoethane}} \text{but-}1\text{-yne}$

Which of the following has acidic hydrogen?

Reactant $P$ (an alkyne) gives products $Q$ (trans-alkene) or $R$ (cis-alkene).
The possible reagents are:
$(I) \ 2Na/liq. NH_3$
$(II) \ H_2/Pd/CaCO_3$ (quinoline)
$(III) \ 2H_2/Pd/C$
Which of the following statements is/are correct with respect to the above conversion?

When acetylene is passed into dilute sulphuric acid containing $Hg^{2+}$ ions,the product formed is

Which of the following reactants exhibits acidic properties?

Give a brief description of the structure of ethyne (acetylene).