Is this a run-on sentence Karen's uncle arrives tomorrow she wants to see him?
Yes. It is a run-on sentence as it lacks necessary punctuation mark or conjunction to separate two sentences it actually it contains: Karen's uncle arrives tomorrow and she wants to see him. To avoid it being run-on sentence, it can be re-written as follows:Karen's uncle arrives tomorrow; She wants to see him.orKaren's uncle arrives tomorrow and she wants to she him.or Karen wants to see her uncle who arrives tomorrow.