What is obtained when chloroform is heated with $Ag$ powder?

Ethyne on reaction with dil. $H_2SO_4$ and $Hg(II)$ gives:

Which of the following is Lindlar catalyst?

Compound $(X)$ [styrene] is subjected to the following sequence of reactions: $(i)$ $Br_2/CHCl_3$, $(ii)$ $NaNH_2$ (excess), $(iii)$ $CH_3I$, $(iv)$ $H_2, Na/NH_3(l)$, giving Major Product $(Y)$. The molar mass of the major product $(Y)$ formed is . . . . . . $\text{g mol}^{-1}$. (Given molar mass in $\text{g mol}^{-1}$: $C:12, H:1$)

What is the increasing order of acidity for the following substances?
$(1)$ $CH_2=CH_2$
$(2)$ $CH_3-CH_3$
$(3)$ $HC \equiv CH$
$(4)$ $NH_3$

$CH \equiv CH \mathop {\xrightarrow{Ni(CN)_2}}\limits_{Pressure} X$. Here,$X$ in the reaction is: