Which gas is used in metal welding?

What are $X$ and $Y$ respectively in the following reactions?
$X + 2D_2O \rightarrow C_2D_2 + P$
$Y + 12D_2O \rightarrow 3CD_4 + Q$

Which of the following compounds do not react with $NaNH_2$? Why?
$CH_3-C \equiv C-CH_3, CH_3-CH_2-C \equiv CH, C_2H_5-C \equiv C-C_2H_5, HC \equiv CH, CH_3-CH=CH_2, CH_2=CH-C \equiv CH$

In the following series of chemical reactions,identify $Z$.
$C_3H_7OH$ $\xrightarrow[160-180\,^{\circ}C]{Conc. H_2SO_4} X$ $\xrightarrow{Br_2} Y$ $\xrightarrow{Excess \ of \ Alc. KOH} Z$

$(A)$ $\xrightarrow[dil. H_2SO_4]{HgSO_4} (B)$ $\xrightarrow{LiAlH_4} \underset{\text{racemic mixture}}{(C)}$
$\therefore$ reactant $(A)$ is

What are $X$ and $Y$ respectively in the following reaction?
$Z$-product $\stackrel{Y}{\longleftarrow} 2$-butyne $\stackrel{X}{\longrightarrow} E$-product