Number of acidic hydrogen atoms in $but-1-yne$ are

What happens when a mixture of acetylene and hydrogen is passed over heated Lindlar's catalyst?

$C_2H_2 \mathop {}$ ${\xrightarrow{{HgSO_4, H_2SO_4}}} A$ $\xrightarrow{{[O]}} B$. $B$ is

$HC\equiv CH + 2HOCl \rightarrow A$. What is the product $A$?

What will be obtained by the reaction of calcium carbide with heavy water? Give its chemical equation.

The relation between $(B)$ and $(C)$ is:
$CH_3-C \equiv CH$ $\xrightarrow{NaNH_2}$ $\xrightarrow{CH_3-I} (A)$ $\xrightarrow{Li/liq. NH_3} (B)$
$CH_3-C \equiv CH$ $\xrightarrow{NaNH_2}$ $\xrightarrow{CH_3-I} (A)$ $\xrightarrow[Pd/CaCO_3]{H_2} (C)$