Concept:Carbon dioxide gas dissolves in water under high pressure, leaving hydrogen gas unabsorbed.
Explanation:Hydrogen is produced industrially from water gas, which contains carbon monoxide and hydrogen.
The carbon monoxide is converted to carbon dioxide using steam:
CO+H2O⇌CO2+H2.
The unwanted
CO2 is removed by washing the gas mixture under pressure.
At high pressure, carbon dioxide dissolves readily in water, whereas hydrogen is almost insoluble and remains as gas.
Drying over phosphorus(V) oxide only removes water vapour, not
CO2.
Passing the mixture through limewater can remove
CO2, but this is not the industrial method used.
Ammoniacal copper(I) chloride is used to absorb carbon monoxide, not carbon dioxide.
Answer:A. washing under pressure