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) $(i)$ Hydrogen economy: It is a technique of using dihydrogen in an efficient way,involving the transportation and storage of dihydrogen in the form of liquid or gas. It is eco-friendly and releases more energy than petrol,making it suitable for use in fuel cells.
$(ii)$ Hydrogenation: It is the addition of dihydrogen to another reactant,typically in the presence of a catalyst,to reduce a compound. For example,the hydrogenation of vegetable oil using nickel as a catalyst produces edible fats.
$(iii)$ Syngas: It is a mixture of carbon monoxide $(CO)$ and dihydrogen $(H_2)$. It is also known as synthesis gas or water gas and is used for the synthesis of methanol. It is produced by the reaction of steam with hydrocarbons or coke at high temperatures: $C_nH_{2n+2} + nH_2O \xrightarrow[Ni]{1270\ K} nCO + (3n+1)H_2$.
$(iv)$ Water-gas shift reaction: It is the reaction of carbon monoxide in syngas with steam in the presence of a catalyst to increase the yield of dihydrogen: $CO_{(g)} + H_2O_{(g)} \xrightarrow[Catalyst]{673\ K} CO_{2_{(g)}} + H_{2_{(g)}}$.
$(v)$ Fuel-cell: These are devices that produce electricity directly from fuels like dihydrogen in the presence of an electrolyte. They are preferred due to their eco-friendly nature and high energy output per unit mass.