Do you think I should consider this sentence (1) as wrong? (I included it in a test) .

1) He tells how his ship was caught in a violent storm, then by mist and snow and finally was surrounded by ice.
2) I need to find a reading comprehension at intermediate level to be included in a one-hour test. Do you have any suggestions?
3) I also need to prepare a sort of English entry test for EFL students (at intermediate level). I wonder if you could help me.

1) He tells how his ship was caught in a violent storm, then by mist and snow and finally was surrounded by ice.

You have a three-part series here, but the second part in the series has no verb. You have this: "caught ... , _____ by mist and snow, and ... surrounded ..." AND PUT THAT COMMA AFTER "snow"!!

I'll look for things for 2 and 3.