Option B – NH3
The ammonia formed is dried using an unusual drying agent – calcium oxide, CaO (quicklime). Calcium oxide reacts with chlorine and carbon dioxide. Hence, it cannot be used for drying chlorine and carbon dioxide. On the other hand, calcium oxide does not react with hydrogen and ammonia gases. Hence, calcium oxide can be used for drying hydrogen and ammonia gases
Ammonia is made commercially by the direct combination of nitrogen and hydrogen using a catalyst – finely reduced (or divided) iron impregnated with aluminium oxide.