"He tells her it is impossible."
Translation:Lui le dice che è impossibile.
I agree with chemacasado. Thinking of it in English, "to tell" someone something implies only the action of communicating something to someone. While the word "inform" implies a more official or formal notification process. Think of it at the DMV line--the clerk could "tell" you it will be impossible for you to pass the test that day because they are closing in 10 minutes and she doesn't think you have time. Conversely, the DMV itself (in its official capacity) can "inform" you that no one else is allowed to start the test that day because there is not sufficient time remaining. See? They sort of, but not exactly, mean the same thing, but their connotations are different.