Formation of ethylene from acetylene is an example of

The number and type of bonds between two carbon atoms in $CaC_2$ are:

The bond length between the hybridized carbon atom and another carbon atom is minimum in:

The catalyst required for the dimerization of acetylene to form chloroprene is ....

Complete the following reactions:
$(1)$ $CH \equiv CH + 2H_2 \xrightarrow[523-573 \ K]{Ni} ?$
$(2)$ $CH_3-C \equiv CH + 2H_2 \xrightarrow[or \ Ni, \Delta]{Pd \ or \ Pt} ?$

One mole of $1,2$-dibromopropane on treatment with $X$ moles of $NaNH_2$ followed by treatment with ethyl bromide gave a pentyne. The value of $X$ is