What is Lindlar's catalyst?

Silver acetylide when heated with $HCl$ gives:

Identify the alkyne in the following sequence of reactions:

Explain: 'Hydrogen attached to a carbon having a triple bond is acidic in nature.' Also,write an appropriate reaction for it.

Which of the following alkynes,upon treatment with $H_2$ $(2 \ mole)$ / $Pt$,gives an optically inactive compound?

An inorganic metal oxide $(A)$ heated with carbon gives compound $(B)$,which on reaction with water gives ethyne. What are the compounds $(A)$ and $(B)$?