Final answer:
The 3rd ghost to visit Scrooge is the Ghost of Christmas Yet to Come, showcasing Scrooge's potential future.
Step-by-step explanation:
The 3rd ghost that comes to visit Scrooge in Charles Dickens' A Christmas Carol is the Ghost of Christmas Yet to Come. This is the final spirit that visits Scrooge, following the Ghost of Christmas Past and the Ghost of Christmas Present.
The purpose of this spectral visitation is to show Scrooge what could happen if he continues on his current path of greed and selfishness.