Final answer:
Pennsylvania is not a city, it is a state. Columbus, Atlanta, and Charleston are cities.
Step-by-step explanation:
The question asks which of the following is not a city:
Columbus, Pennsylvania, Atlanta, Charleston.
The answer to this question is Pennsylvania, which is not a city, but rather a state in the United States of America.
Columbus is the capital city of Ohio, Atlanta is the capital and the most populous city of the state of Georgia, and Charleston is the largest city in the state of South Carolina.