What is the product formed when two molecules of $HBr$ are added to $CH_3 - C \equiv CH$?

The correct order for acid strength of compounds $CH \equiv CH$,$CH_3 - C \equiv CH$,and $CH_2 = CH_2$ is as follows:

$[P]$ $\xrightarrow{Br_{2}} C_{2}H_{4}Br_{2}$ $\xrightarrow{NaNH_{2}/NH_{3}} [Q]$
$[Q]$ $\xrightarrow{20 \% H_{2}SO_{4}, Hg^{2+}, \Delta} [R]$ $\xrightarrow{Zn-Hg/HCl} [S]$
The species $[P], [Q], [R]$ and $[S]$ respectively are:

Which of the following metal carbides gives propyne on hydrolysis?

$A$ hydrocarbon $X$ with molecular formula $C_4H_6$ decolourises bromine water and forms a white precipitate in ethanolic $AgNO_3$ solution. Treatment of $X$ with $HgCl_2$ in aqueous $H_2SO_4$ produces a compound,which gives a yellow precipitate when treated with $I_2$ and $NaOH$. The structure of $X$ is

Acetylene can be obtained by the reaction: