I hope/assume that everyone is rooting for Nigeria in this one?
Nigeria will qualify with a win over Argentina. A point would be enough if Iceland do not beat Croatia.
If Argentina and Nigeria draw, Iceland will make the last 16 if they beat Croatia by a two-goal margin and also score at least one more than Nigeria.
Argentina will qualify with victory over Nigeria coupled with Iceland failing to defeat Croatia. If Iceland do beat Croatia, then Jorge Sampaoli's side can still qualify if they beat Nigeria by two more goals than Iceland win their game. If Argentina and Iceland win and finish with identical records their fate will be decided by their disciplinary records and then the drawing of lots. Argentina have picked up three yellow cards and Iceland have none