Acetylene reacts with $HCN$ in the presence of $Ba(CN)_2$ to yield

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

When calcium carbide is added to water,the gas that is evolved is

Acetylene gas when passed through $20\% \ H_2SO_4$ at $80 \, ^\circ C$ gives acetaldehyde. The catalyst required for this conversion is:

The reaction of silver powder with chloroform produces $....$.

Reactant $P$ (an alkyne) gives products $Q$ (trans-alkene) or $R$ (cis-alkene).
The possible reagents are:
$(I) \ 2Na/liq. NH_3$
$(II) \ H_2/Pd/CaCO_3$ (quinoline)
$(III) \ 2H_2/Pd/C$
Which of the following statements is/are correct with respect to the above conversion?