inform on someone
to tell the authorities about someone; to tattle on someone. I am going to have to inform on you. Liz informed on Ken to their mother.
inform someone about someone or something
to tell someone about someone or something. How is my friend Tom getting on? I asked you to inform me about him from time to time. Please inform me about the state of the contract for the book.
inform someone of something
to tell someone a fact. Please inform Sally of my decision. Sally has been informed of your decision.
inform someone on someone
to tattle (on someone) (to someone). I will inform the teacher on you! Billy informed his mother on Bobby.