They're all fine. A desert island is an uninhabited island. A deserted island is one that had been inhabited, but everyone has left or died. 'To chance upon' means to find or meet unexpectedly, so you don't need to add the word 'meet'.

deserted

Is it interesting to live in Canada? In which country would you like to live? What made you learn English? All criminals should be sent to a desert island. AT the shop TODAY, I chanced upon MEETING my old teacher. Great job! Alot of these sentences are correct. Any corrections are in CAPS