How many isomers are possible for pentyne $(C_5H_8)$?

Which of the following is suitable for the preparation of alkene from alkyne?

$CH_3-CH_2-CH_2-C \equiv CH \xrightarrow[\text{Excess}]{HCl} ?$

Consider the following sequence,where $A$ can be:
$A$ $(C_{3}H_{6}Cl_{2})$ $\xrightarrow[2. \, H^{+} \, (mild)]{1. \, \text{alcoholic } KOH / \Delta, \text{ followed by } NaNH_{2} / \Delta}$ $B$ $\xrightarrow[H_{2}O_{2} / OH^{-}]{B_{2}H_{6}}$ $C$
$A$ $\xrightarrow{aq. \, KOH \, (excess)}$ $C$
Identify $A$.

Identify $X$ in the following sequence of reactions.
$CH_3-CH(Br)-CH(Br)-CH_2-CH_2-CH_3 \xrightarrow[(ii) Na \text{ in liquid } NH_3]{(i) NaNH_2} X$

Acetylene does not react with .....