Which of the following is a homologue of ethyne?

Chloroform,on warming with $Ag$ powder,gives:

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

The homologue of ethyne is

Which of the following is used to distinguish ethylene and acetylene?

$HC \equiv CNa + Cl - CH_2 - CH_2 - CH_2 - I \to (A)$; Major product $(A)$ is