Note: Australia is generally considered to be a continental landmass, rather than an island. If however one does count Australia among the islands it, not Greenland, would be the largest in the world (unless one also considered Antarctica an island).
... refers to the fourth case--that is, the dative). Incidentally, "tatpurusha" is a tatpurusha ("this man"--meaning someone's agent), while "caturtitatpurusha" is ...