Necessary is a synonym of Inevitable. Inevitable is the opposite of Possible. 
Unfold is a synonym of Expand. Gas can Expand. Gas is related to Commodity. Commodity is related to Gold. 
Necessary <--Synonym--> Inevitable <--Antonym--> Possible 
Unfold <--Synonym--> Expand <--CapableOf-- Gas <--RelatedTo--> Commodity <--RelatedTo--> Gold 