which complex sentence is punctuated correctly?\nwhen your favorite song comes on let me know.\ncharlotte…

Brief Explanations:

In a complex - sentence, when the subordinate clause comes before the main clause, it should be followed by a comma. In the first option, there should be a comma after "comes on". In the second option, it is a fragment. The third option has the wrong placement of the comma (it should not be between the subject and the verb in the main clause). The fourth option has the subordinate clause "If you need a ride home" followed by a comma before the main clause "Julian will be driving", which is correct punctuation.

Answer:

If you need a ride home, Julian will be driving.