Oxidation state of hydrogen in compound $X$ is $-1$ and in compound $Y$ is $+1$. $X$ and $Y$ are respectively

Identify the reactions in which $H_2$ is liberated? $(i)$ $Zn + NaOH_{(aq)} \longrightarrow$ $(ii)$ $HCOOH \xrightarrow[\text{Conc. } H_2SO_4]{373 \ K}$ $(iii)$ $CH_{4(g)} + H_2O_{(g)} \xrightarrow[Ni]{1270 \ K}$ $(iv)$ $Zn + H^+_{(aq)} \longrightarrow$ $(v)$ $C_{(s)} + H_2O_{(g)} \xrightarrow{1270 \ K}$

Which of the following is a hydride?

What is Carbogen?

When electric current is passed through an ionic hydride in the molten state,

The basic principle of the hydrogen economy is the transportation and storage of energy in the form of liquid or gaseous hydrogen. Which property of hydrogen may be useful for this purpose? Support your answer with a chemical equation if required.