Hydrogen is essential in an Electrolux refrigeration system, because
(a) It acts as a catalyst in the evaporator
(b) The reaction between hydrogen and ammonia is endothermic in evaporator and exothermic in absorber
(c) The cooled hydrogen leaving the heat exchanger cools the refrigerant entering the evaporator
(d) It helps in maintaining a low partial pressure for the evaporating ammonia