What do you understand by the terms: $(i)$ hydrogen economy,$(ii)$ hydrogenation,$(iii)$ syngas,$(iv)$ water-gas shift reaction,and $(v)$ fuel-cell?

(N/A) $(i)$ $\text{Hydrogen economy}$: The basic principle of hydrogen economy is the storage and transportation of energy in the form of liquid or gaseous dihydrogen.
$(ii)$ $\text{Hydrogenation}$: The process of adding dihydrogen to unsaturated organic compounds in the presence of catalysts to form saturated compounds.
$(iii)$ $\text{Syngas}$: $A$ mixture of $CO$ and $H_2$ is called synthesis gas or syngas.
$(iv)$ $\text{Water-gas shift reaction}$: The reaction of carbon monoxide of syngas with steam in the presence of a catalyst $(FeCrO_4)$ to increase the production of dihydrogen: $CO_{(g)} + H_2O_{(g)} \xrightarrow[673 \ K]{\text{catalyst}} CO_{2(g)} + H_{2(g)}$.
$(v)$ $\text{Fuel-cell}$: $A$ device that converts the chemical energy of a fuel (like hydrogen,methane,methanol) directly into electrical energy.